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 $45.53   13.559%   $51.7034   $51.70   $51.70   $51.70  
  Purchase #2 $189.58   8.605%   $205.8934   $205.89   $205.90   $205.90  
  Purchase #3 $115.79   8.561%   $125.7028   $125.70   $125.70   $125.70  
  Purchase #4 $135.49   8.164%   $146.5514   $146.55   $146.55   $146.60  
  Purchase #5 $250.73   10.205%   $276.317   $276.32   $276.30   $276.30  
  Purchase #6 $126.52   8.833%   $137.6955   $137.70   $137.70   $137.70  
  Purchase #7 $212.49   6.577%   $226.4655   $226.47   $226.45   $226.50  
  7 purchase totals = $1,076.13       $1,170.3290   $1,170.33   $1,170.30   $1,170.40