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 $204.39   11.419%   $227.7293   $227.73   $227.75   $227.70  
  Purchase #2 $189.54   10.502%   $209.4455   $209.45   $209.45   $209.40  
  Purchase #3 $187.78   7.870%   $202.5583   $202.56   $202.55   $202.60  
  Purchase #4 $240.29   5.275%   $252.9653   $252.97   $252.95   $253.00  
  Purchase #5 $66.66   8.571%   $72.3734   $72.37   $72.35   $72.40  
  Purchase #6 $242.80   11.663%   $271.1178   $271.12   $271.10   $271.10  
  Purchase #7 $75.28   10.364%   $83.082   $83.08   $83.10   $83.10  
  7 purchase totals = $1,206.74       $1,319.2716   $1,319.28   $1,319.25   $1,319.30