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 $64.65   10.681%   $71.5553   $71.56   $71.55   $71.60  
  Purchase #2 $242.92   8.153%   $262.7253   $262.73   $262.75   $262.70  
  Purchase #3 $42.59   12.755%   $48.0224   $48.02   $48.00   $48.00  
  Purchase #4 $162.91   9.612%   $178.5689   $178.57   $178.55   $178.60  
  Purchase #5 $185.78   13.722%   $211.2727   $211.27   $211.25   $211.30  
  Purchase #6 $177.57   3.662%   $184.0726   $184.07   $184.05   $184.10  
  Purchase #7 $95.42   8.302%   $103.3418   $103.34   $103.35   $103.30  
  7 purchase totals = $971.84       $1,059.5590   $1,059.56   $1,059.50   $1,059.60