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 $168.84   13.395%   $191.4561   $191.46   $191.45   $191.50  
  Purchase #2 $126.54   7.412%   $135.9191   $135.92   $135.90   $135.90  
  Purchase #3 $111.39   5.113%   $117.0854   $117.09   $117.10   $117.10  
  Purchase #4 $67.45   11.275%   $75.055   $75.06   $75.05   $75.10  
  Purchase #5 $220.31   5.297%   $231.9798   $231.98   $232.00   $232.00  
  Purchase #6 $73.58   13.252%   $83.3308   $83.33   $83.35   $83.30  
  Purchase #7 $179.98   3.502%   $186.2829   $186.28   $186.30   $186.30  
  7 purchase totals = $948.09       $1,021.1091   $1,021.12   $1,021.15   $1,021.20