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 $194.58   7.733%   $209.6269   $209.63   $209.65   $209.60  
  Purchase #2 $150.35   13.446%   $170.5661   $170.57   $170.55   $170.60  
  Purchase #3 $136.35   10.206%   $150.2659   $150.27   $150.25   $150.30  
  Purchase #4 $71.80   4.567%   $75.0791   $75.08   $75.10   $75.10  
  Purchase #5 $234.40   7.335%   $251.5932   $251.59   $251.60   $251.60  
  Purchase #6 $138.46   11.309%   $154.1184   $154.12   $154.10   $154.10  
  Purchase #7 $22.46   8.835%   $24.4443   $24.44   $24.45   $24.40  
  7 purchase totals = $948.40       $1,035.6939   $1,035.70   $1,035.70   $1,035.70