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 $113.59   11.462%   $126.6097   $126.61   $126.60   $126.60  
  Purchase #2 $60.87   6.343%   $64.731   $64.73   $64.75   $64.70  
  Purchase #3 $121.40   6.185%   $128.9086   $128.91   $128.90   $128.90  
  Purchase #4 $48.38   6.863%   $51.7003   $51.70   $51.70   $51.70  
  Purchase #5 $102.86   9.244%   $112.3684   $112.37   $112.35   $112.40  
  Purchase #6 $239.69   9.313%   $262.0123   $262.01   $262.00   $262.00  
  Purchase #7 $216.62   3.246%   $223.6515   $223.65   $223.65   $223.70  
  7 purchase totals = $903.41       $969.9818   $969.98   $969.95   $970.00