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 $214.70   12.577%   $241.7028   $241.70   $241.70   $241.70  
  Purchase #2 $177.78   5.653%   $187.8299   $187.83   $187.85   $187.80  
  Purchase #3 $144.42   4.484%   $150.8958   $150.90   $150.90   $150.90  
  Purchase #4 $157.73   3.830%   $163.7711   $163.77   $163.75   $163.80  
  Purchase #5 $6.52   11.248%   $7.2534   $7.25   $7.25   $7.30  
  Purchase #6 $122.74   8.834%   $133.5829   $133.58   $133.60   $133.60  
  Purchase #7 $138.25   9.674%   $151.6243   $151.62   $151.60   $151.60  
  7 purchase totals = $962.14       $1,036.6602   $1,036.65   $1,036.65   $1,036.70