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 $74.47   12.722%   $83.9441   $83.94   $83.95   $83.90  
  Purchase #2 $223.92   9.388%   $244.9416   $244.94   $244.95   $244.90  
  Purchase #3 $148.33   6.640%   $158.1791   $158.18   $158.20   $158.20  
  Purchase #4 $58.58   5.467%   $61.7826   $61.78   $61.80   $61.80  
  Purchase #5 $64.62   10.809%   $71.6048   $71.60   $71.60   $71.60  
  Purchase #6 $77.77   7.374%   $83.5048   $83.50   $83.50   $83.50  
  Purchase #7 $8.95   6.612%   $9.5418   $9.54   $9.55   $9.50  
  7 purchase totals = $656.64       $713.4988   $713.48   $713.55   $713.40