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 $102.84   7.706%   $110.7649   $110.76   $110.75   $110.80  
  Purchase #2 $165.89   13.238%   $187.8505   $187.85   $187.85   $187.90  
  Purchase #3 $193.76   12.285%   $217.5634   $217.56   $217.55   $217.60  
  Purchase #4 $125.85   8.694%   $136.7914   $136.79   $136.80   $136.80  
  Purchase #5 $189.45   9.191%   $206.8623   $206.86   $206.85   $206.90  
  Purchase #6 $231.30   9.562%   $253.4169   $253.42   $253.40   $253.40  
  Purchase #7 $129.77   8.169%   $140.3709   $140.37   $140.35   $140.40  
  7 purchase totals = $1,138.86       $1,253.6203   $1,253.61   $1,253.55   $1,253.80