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 $76.74   11.434%   $85.5145   $85.51   $85.50   $85.50  
  Purchase #2 $64.39   10.404%   $71.0891   $71.09   $71.10   $71.10  
  Purchase #3 $107.54   5.762%   $113.7365   $113.74   $113.75   $113.70  
  Purchase #4 $73.83   11.539%   $82.3492   $82.35   $82.35   $82.30  
  Purchase #5 $97.99   3.201%   $101.1267   $101.13   $101.15   $101.10  
  Purchase #6 $209.88   3.239%   $216.678   $216.68   $216.70   $216.70  
  Purchase #7 $247.85   10.165%   $273.044   $273.04   $273.05   $273.00  
  7 purchase totals = $878.22       $943.5380   $943.54   $943.60   $943.40