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 $66.90   10.313%   $73.7994   $73.80   $73.80   $73.80  
  Purchase #2 $244.39   4.478%   $255.3338   $255.33   $255.35   $255.30  
  Purchase #3 $151.43   12.536%   $170.4133   $170.41   $170.40   $170.40  
  Purchase #4 $183.48   10.405%   $202.5711   $202.57   $202.55   $202.60  
  Purchase #5 $217.60   13.465%   $246.8998   $246.90   $246.90   $246.90  
  Purchase #6 $208.87   5.829%   $221.045   $221.05   $221.05   $221.00  
  Purchase #7 $187.91   8.310%   $203.5253   $203.53   $203.55   $203.50  
  7 purchase totals = $1,260.58       $1,373.5877   $1,373.59   $1,373.60   $1,373.50