Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $102.86   11.283%   $114.4657   $114.47   $114.45   $114.50  
  Purchase #2 $153.60   9.298%   $167.8817   $167.88   $167.90   $167.90  
  Purchase #3 $250.47   10.649%   $277.1426   $277.14   $277.15   $277.10  
  Purchase #4 $203.64   10.430%   $224.8797   $224.88   $224.90   $224.90  
  Purchase #5 $165.52   4.399%   $172.8012   $172.80   $172.80   $172.80  
  Purchase #6 $226.88   6.129%   $240.7855   $240.79   $240.80   $240.80  
  Purchase #7 $243.97   7.143%   $261.3968   $261.40   $261.40   $261.40  
  7 purchase totals = $1,346.94       $1,459.3532   $1,459.36   $1,459.40   $1,459.40