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 $136.66   12.452%   $153.6769   $153.68   $153.70   $153.70  
  Purchase #2 $236.30   4.479%   $246.8839   $246.88   $246.90   $246.90  
  Purchase #3 $16.32   10.640%   $18.0564   $18.06   $18.05   $18.10  
  Purchase #4 $15.87   6.577%   $16.9138   $16.91   $16.90   $16.90  
  Purchase #5 $164.66   6.719%   $175.7235   $175.72   $175.70   $175.70  
  Purchase #6 $221.52   11.114%   $246.1397   $246.14   $246.15   $246.10  
  Purchase #7 $174.84   8.146%   $189.0825   $189.08   $189.10   $189.10  
  7 purchase totals = $966.17       $1,046.4767   $1,046.47   $1,046.50   $1,046.50