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 $52.29   7.458%   $56.1898   $56.19   $56.20   $56.20  
  Purchase #2 $229.73   10.835%   $254.6212   $254.62   $254.60   $254.60  
  Purchase #3 $163.50   8.244%   $176.9789   $176.98   $177.00   $177.00  
  Purchase #4 $205.37   6.748%   $219.2284   $219.23   $219.25   $219.20  
  Purchase #5 $57.74   3.748%   $59.9041   $59.90   $59.90   $59.90  
  Purchase #6 $78.58   6.672%   $83.8229   $83.82   $83.80   $83.80  
  Purchase #7 $234.79   5.637%   $248.0251   $248.03   $248.05   $248.00  
  7 purchase totals = $1,022.00       $1,098.7704   $1,098.77   $1,098.80   $1,098.70