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 $48.26   9.824%   $53.0011   $53.00   $53.00   $53.00  
  Purchase #2 $89.79   7.266%   $96.3141   $96.31   $96.30   $96.30  
  Purchase #3 $49.62   6.803%   $52.9956   $53.00   $53.00   $53.00  
  Purchase #4 $115.41   8.337%   $125.0317   $125.03   $125.05   $125.00  
  Purchase #5 $7.84   6.240%   $8.3292   $8.33   $8.35   $8.30  
  Purchase #6 $182.25   12.229%   $204.5374   $204.54   $204.55   $204.50  
  Purchase #7 $197.52   5.845%   $209.065   $209.07   $209.05   $209.10  
  7 purchase totals = $690.69       $749.2741   $749.28   $749.30   $749.20