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 $96.98   11.559%   $108.1899   $108.19   $108.20   $108.20  
  Purchase #2 $221.52   8.139%   $239.5495   $239.55   $239.55   $239.50  
  Purchase #3 $157.30   4.820%   $164.8819   $164.88   $164.90   $164.90  
  Purchase #4 $155.68   9.593%   $170.6144   $170.61   $170.60   $170.60  
  Purchase #5 $215.65   11.484%   $240.4152   $240.42   $240.40   $240.40  
  Purchase #6 $60.85   5.587%   $64.2497   $64.25   $64.25   $64.20  
  Purchase #7 $62.78   4.374%   $65.526   $65.53   $65.55   $65.50  
  7 purchase totals = $970.76       $1,053.4266   $1,053.43   $1,053.45   $1,053.30