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 $158.47   11.780%   $177.1378   $177.14   $177.15   $177.10  
  Purchase #2 $54.91   10.678%   $60.7733   $60.77   $60.75   $60.80  
  Purchase #3 $18.77   8.152%   $20.3001   $20.30   $20.30   $20.30  
  Purchase #4 $174.27   8.532%   $189.1387   $189.14   $189.15   $189.10  
  Purchase #5 $82.85   3.110%   $85.4266   $85.43   $85.45   $85.40  
  Purchase #6 $171.35   7.580%   $184.3383   $184.34   $184.35   $184.30  
  Purchase #7 $63.90   3.251%   $65.9774   $65.98   $66.00   $66.00  
  7 purchase totals = $724.52       $783.0922   $783.10   $783.15   $783.00