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 $32.61   3.448%   $33.7344   $33.73   $33.75   $33.70  
  Purchase #2 $75.55   7.581%   $81.2774   $81.28   $81.30   $81.30  
  Purchase #3 $96.54   11.533%   $107.674   $107.67   $107.65   $107.70  
  Purchase #4 $178.67   6.866%   $190.9375   $190.94   $190.95   $190.90  
  Purchase #5 $156.50   11.300%   $174.1845   $174.18   $174.20   $174.20  
  Purchase #6 $181.40   6.640%   $193.445   $193.45   $193.45   $193.40  
  Purchase #7 $229.65   12.111%   $257.4629   $257.46   $257.45   $257.50  
  7 purchase totals = $950.92       $1,038.7157   $1,038.71   $1,038.75   $1,038.70