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 $179.79   13.556%   $204.1623   $204.16   $204.15   $204.20  
  Purchase #2 $125.84   8.588%   $136.6471   $136.65   $136.65   $136.60  
  Purchase #3 $67.43   12.573%   $75.908   $75.91   $75.90   $75.90  
  Purchase #4 $229.85   6.340%   $244.4225   $244.42   $244.40   $244.40  
  Purchase #5 $120.32   3.794%   $124.8849   $124.88   $124.90   $124.90  
  Purchase #6 $61.66   4.710%   $64.5642   $64.56   $64.55   $64.60  
  Purchase #7 $193.96   11.684%   $216.6223   $216.62   $216.60   $216.60  
  7 purchase totals = $978.85       $1,067.2113   $1,067.20   $1,067.15   $1,067.20