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 $62.55   7.421%   $67.1918   $67.19   $67.20   $67.20  
  Purchase #2 $150.49   4.295%   $156.9535   $156.95   $156.95   $157.00  
  Purchase #3 $95.44   4.416%   $99.6546   $99.65   $99.65   $99.70  
  Purchase #4 $89.75   8.557%   $97.4299   $97.43   $97.45   $97.40  
  Purchase #5 $108.88   11.746%   $121.669   $121.67   $121.65   $121.70  
  Purchase #6 $115.48   11.633%   $128.9138   $128.91   $128.90   $128.90  
  Purchase #7 $118.57   5.512%   $125.1056   $125.11   $125.10   $125.10  
  7 purchase totals = $741.16       $796.9182   $796.91   $796.90   $797.00