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 $180.58   9.558%   $197.8398   $197.84   $197.85   $197.80  
  Purchase #2 $35.95   8.214%   $38.9029   $38.90   $38.90   $38.90  
  Purchase #3 $137.56   3.477%   $142.343   $142.34   $142.35   $142.30  
  Purchase #4 $76.93   10.718%   $85.1754   $85.18   $85.20   $85.20  
  Purchase #5 $137.77   6.276%   $146.4164   $146.42   $146.40   $146.40  
  Purchase #6 $200.31   9.341%   $219.021   $219.02   $219.00   $219.00  
  Purchase #7 $98.95   5.470%   $104.3626   $104.36   $104.35   $104.40  
  7 purchase totals = $868.05       $934.0611   $934.06   $934.05   $934.00