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 $40.28   9.289%   $44.0216   $44.02   $44.00   $44.00  
  Purchase #2 $195.32   3.190%   $201.5507   $201.55   $201.55   $201.60  
  Purchase #3 $242.68   11.398%   $270.3407   $270.34   $270.35   $270.30  
  Purchase #4 $182.46   11.711%   $203.8279   $203.83   $203.85   $203.80  
  Purchase #5 $82.37   9.121%   $89.883   $89.88   $89.90   $89.90  
  Purchase #6 $213.86   4.358%   $223.18   $223.18   $223.20   $223.20  
  Purchase #7 $129.39   3.578%   $134.0196   $134.02   $134.00   $134.00  
  7 purchase totals = $1,086.36       $1,166.8235   $1,166.82   $1,166.85   $1,166.80