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 $56.95   5.480%   $60.0709   $60.07   $60.05   $60.10  
  Purchase #2 $232.98   11.668%   $260.1641   $260.16   $260.15   $260.20  
  Purchase #3 $172.52   5.677%   $182.314   $182.31   $182.30   $182.30  
  Purchase #4 $236.72   8.339%   $256.4601   $256.46   $256.45   $256.50  
  Purchase #5 $21.42   13.145%   $24.2357   $24.24   $24.25   $24.20  
  Purchase #6 $183.54   7.415%   $197.1495   $197.15   $197.15   $197.10  
  Purchase #7 $179.71   3.748%   $186.4455   $186.45   $186.45   $186.40  
  7 purchase totals = $1,083.84       $1,166.8398   $1,166.84   $1,166.80   $1,166.80