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 $47.41   13.215%   $53.6752   $53.68   $53.70   $53.70  
  Purchase #2 $221.85   10.340%   $244.7893   $244.79   $244.80   $244.80  
  Purchase #3 $106.33   10.751%   $117.7615   $117.76   $117.75   $117.80  
  Purchase #4 $107.94   10.550%   $119.3277   $119.33   $119.35   $119.30  
  Purchase #5 $231.49   10.490%   $255.7733   $255.77   $255.75   $255.80  
  Purchase #6 $247.66   9.197%   $270.4373   $270.44   $270.45   $270.40  
  Purchase #7 $28.80   13.291%   $32.6278   $32.63   $32.65   $32.60  
  7 purchase totals = $991.48       $1,094.3921   $1,094.40   $1,094.45   $1,094.40