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 $68.39   11.841%   $76.4881   $76.49   $76.50   $76.50  
  Purchase #2 $45.88   12.677%   $51.6962   $51.70   $51.70   $51.70  
  Purchase #3 $250.50   10.638%   $277.1482   $277.15   $277.15   $277.10  
  Purchase #4 $94.58   5.450%   $99.7346   $99.73   $99.75   $99.70  
  Purchase #5 $52.55   7.197%   $56.332   $56.33   $56.35   $56.30  
  Purchase #6 $196.86   12.834%   $222.125   $222.13   $222.15   $222.10  
  Purchase #7 $38.67   6.672%   $41.2501   $41.25   $41.25   $41.30  
  7 purchase totals = $747.43       $824.7742   $824.78   $824.85   $824.70