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 $234.84   10.267%   $258.951   $258.95   $258.95   $259.00  
  Purchase #2 $213.59   12.633%   $240.5728   $240.57   $240.55   $240.60  
  Purchase #3 $201.54   13.804%   $229.3606   $229.36   $229.35   $229.40  
  Purchase #4 $127.29   3.837%   $132.1741   $132.17   $132.15   $132.20  
  Purchase #5 $191.52   8.644%   $208.075   $208.08   $208.10   $208.10  
  Purchase #6 $215.54   11.245%   $239.7775   $239.78   $239.80   $239.80  
  Purchase #7 $153.61   12.338%   $172.5624   $172.56   $172.55   $172.60  
  7 purchase totals = $1,337.93       $1,481.4734   $1,481.47   $1,481.45   $1,481.70