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 $187.39   11.665%   $209.249   $209.25   $209.25   $209.20  
  Purchase #2 $207.53   9.635%   $227.5255   $227.53   $227.55   $227.50  
  Purchase #3 $241.53   12.828%   $272.5135   $272.51   $272.50   $272.50  
  Purchase #4 $202.84   4.221%   $211.4019   $211.40   $211.40   $211.40  
  Purchase #5 $153.61   4.857%   $161.0708   $161.07   $161.05   $161.10  
  Purchase #6 $53.97   9.253%   $58.9638   $58.96   $58.95   $59.00  
  Purchase #7 $77.48   11.453%   $86.3538   $86.35   $86.35   $86.40  
  7 purchase totals = $1,124.35       $1,227.0783   $1,227.07   $1,227.05   $1,227.10