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 $82.91   10.456%   $91.5791   $91.58   $91.60   $91.60  
  Purchase #2 $92.89   11.339%   $103.4228   $103.42   $103.40   $103.40  
  Purchase #3 $61.52   9.252%   $67.2118   $67.21   $67.20   $67.20  
  Purchase #4 $241.98   7.719%   $260.6584   $260.66   $260.65   $260.70  
  Purchase #5 $180.53   13.749%   $205.3511   $205.35   $205.35   $205.40  
  Purchase #6 $49.59   12.320%   $55.6995   $55.70   $55.70   $55.70  
  Purchase #7 $170.94   4.546%   $178.7109   $178.71   $178.70   $178.70  
  7 purchase totals = $880.36       $962.6336   $962.63   $962.60   $962.70