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 $119.97   6.348%   $127.5857   $127.59   $127.60   $127.60  
  Purchase #2 $244.93   12.797%   $276.2737   $276.27   $276.25   $276.30  
  Purchase #3 $238.39   9.729%   $261.583   $261.58   $261.60   $261.60  
  Purchase #4 $138.72   5.736%   $146.677   $146.68   $146.70   $146.70  
  Purchase #5 $12.85   6.148%   $13.64   $13.64   $13.65   $13.60  
  Purchase #6 $196.74   5.442%   $207.4466   $207.45   $207.45   $207.40  
  Purchase #7 $150.26   13.669%   $170.799   $170.80   $170.80   $170.80  
  7 purchase totals = $1,101.86       $1,204.0050   $1,204.01   $1,204.05   $1,204.00