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 $207.34   9.755%   $227.566   $227.57   $227.55   $227.60  
  Purchase #2 $219.82   7.375%   $236.0317   $236.03   $236.05   $236.00  
  Purchase #3 $143.63   9.199%   $156.8425   $156.84   $156.85   $156.80  
  Purchase #4 $230.72   4.115%   $240.2141   $240.21   $240.20   $240.20  
  Purchase #5 $125.28   13.794%   $142.5611   $142.56   $142.55   $142.60  
  Purchase #6 $152.56   5.604%   $161.1095   $161.11   $161.10   $161.10  
  Purchase #7 $72.69   6.543%   $77.4461   $77.45   $77.45   $77.40  
  7 purchase totals = $1,152.04       $1,241.7710   $1,241.77   $1,241.75   $1,241.70