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 $42.46   3.587%   $43.983   $43.98   $44.00   $44.00  
  Purchase #2 $234.55   9.507%   $256.8487   $256.85   $256.85   $256.80  
  Purchase #3 $174.79   9.413%   $191.243   $191.24   $191.25   $191.20  
  Purchase #4 $62.34   8.781%   $67.8141   $67.81   $67.80   $67.80  
  Purchase #5 $181.57   12.175%   $203.6761   $203.68   $203.70   $203.70  
  Purchase #6 $33.71   13.111%   $38.1297   $38.13   $38.15   $38.10  
  Purchase #7 $152.66   11.711%   $170.538   $170.54   $170.55   $170.50  
  7 purchase totals = $882.08       $972.2326   $972.23   $972.30   $972.10