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 $33.54   3.737%   $34.7934   $34.79   $34.80   $34.80  
  Purchase #2 $235.65   12.699%   $265.5752   $265.58   $265.60   $265.60  
  Purchase #3 $250.49   10.777%   $277.4853   $277.49   $277.50   $277.50  
  Purchase #4 $132.71   10.703%   $146.914   $146.91   $146.90   $146.90  
  Purchase #5 $26.71   6.420%   $28.4248   $28.42   $28.40   $28.40  
  Purchase #6 $153.39   8.860%   $166.9804   $166.98   $167.00   $167.00  
  Purchase #7 $78.43   6.700%   $83.6848   $83.68   $83.70   $83.70  
  7 purchase totals = $910.92       $1,003.8579   $1,003.85   $1,003.90   $1,003.90