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 $143.69   13.195%   $162.6499   $162.65   $162.65   $162.60  
  Purchase #2 $53.52   7.873%   $57.7336   $57.73   $57.75   $57.70  
  Purchase #3 $218.76   7.602%   $235.3901   $235.39   $235.40   $235.40  
  Purchase #4 $55.51   9.667%   $60.8762   $60.88   $60.90   $60.90  
  Purchase #5 $75.51   11.473%   $84.1733   $84.17   $84.15   $84.20  
  Purchase #6 $193.74   5.719%   $204.82   $204.82   $204.80   $204.80  
  Purchase #7 $234.92   8.104%   $253.9579   $253.96   $253.95   $254.00  
  7 purchase totals = $975.65       $1,059.6010   $1,059.60   $1,059.60   $1,059.60