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 $150.79   10.505%   $166.6305   $166.63   $166.65   $166.60  
  Purchase #2 $129.97   6.642%   $138.6026   $138.60   $138.60   $138.60  
  Purchase #3 $167.64   13.628%   $190.486   $190.49   $190.50   $190.50  
  Purchase #4 $161.29   8.361%   $174.7755   $174.78   $174.80   $174.80  
  Purchase #5 $121.31   4.703%   $127.0152   $127.02   $127.00   $127.00  
  Purchase #6 $80.96   4.228%   $84.383   $84.38   $84.40   $84.40  
  Purchase #7 $68.34   8.735%   $74.3095   $74.31   $74.30   $74.30  
  7 purchase totals = $880.30       $956.2023   $956.21   $956.25   $956.20