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 $176.27   10.436%   $194.6655   $194.67   $194.65   $194.70  
  Purchase #2 $90.36   6.657%   $96.3753   $96.38   $96.40   $96.40  
  Purchase #3 $88.83   7.692%   $95.6628   $95.66   $95.65   $95.70  
  Purchase #4 $53.55   11.594%   $59.7586   $59.76   $59.75   $59.80  
  Purchase #5 $179.39   12.794%   $202.3412   $202.34   $202.35   $202.30  
  Purchase #6 $56.50   4.153%   $58.8464   $58.85   $58.85   $58.80  
  Purchase #7 $67.81   8.429%   $73.5257   $73.53   $73.55   $73.50  
  7 purchase totals = $712.71       $781.1755   $781.19   $781.20   $781.20