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 $85.55   9.790%   $93.9253   $93.93   $93.95   $93.90  
  Purchase #2 $158.71   13.620%   $180.3263   $180.33   $180.35   $180.30  
  Purchase #3 $240.88   11.838%   $269.3954   $269.40   $269.40   $269.40  
  Purchase #4 $182.38   11.258%   $202.9123   $202.91   $202.90   $202.90  
  Purchase #5 $55.95   3.643%   $57.9883   $57.99   $58.00   $58.00  
  Purchase #6 $237.70   8.619%   $258.1874   $258.19   $258.20   $258.20  
  Purchase #7 $74.79   8.346%   $81.032   $81.03   $81.05   $81.00  
  7 purchase totals = $1,035.96       $1,143.7670   $1,143.78   $1,143.85   $1,143.70