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 $92.73   13.183%   $104.9546   $104.95   $104.95   $105.00  
  Purchase #2 $87.59   4.289%   $91.3467   $91.35   $91.35   $91.30  
  Purchase #3 $83.37   13.868%   $94.9318   $94.93   $94.95   $94.90  
  Purchase #4 $197.66   4.182%   $205.9261   $205.93   $205.95   $205.90  
  Purchase #5 $131.76   3.208%   $135.9869   $135.99   $136.00   $136.00  
  Purchase #6 $228.78   3.607%   $237.0321   $237.03   $237.05   $237.00  
  Purchase #7 $120.67   3.850%   $125.3158   $125.32   $125.30   $125.30  
  7 purchase totals = $942.56       $995.4940   $995.50   $995.55   $995.40