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 $55.52   13.350%   $62.9319   $62.93   $62.95   $62.90  
  Purchase #2 $227.56   13.798%   $258.9587   $258.96   $258.95   $259.00  
  Purchase #3 $148.48   3.206%   $153.2403   $153.24   $153.25   $153.20  
  Purchase #4 $135.80   6.405%   $144.498   $144.50   $144.50   $144.50  
  Purchase #5 $108.64   7.131%   $116.3871   $116.39   $116.40   $116.40  
  Purchase #6 $42.47   8.415%   $46.0439   $46.04   $46.05   $46.00  
  Purchase #7 $220.82   8.682%   $239.9916   $239.99   $240.00   $240.00  
  7 purchase totals = $939.29       $1,022.0515   $1,022.05   $1,022.10   $1,022.00