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 $176.44   8.360%   $191.1904   $191.19   $191.20   $191.20  
  Purchase #2 $159.97   10.173%   $176.2437   $176.24   $176.25   $176.20  
  Purchase #3 $46.42   13.148%   $52.5233   $52.52   $52.50   $52.50  
  Purchase #4 $139.35   13.826%   $158.6165   $158.62   $158.60   $158.60  
  Purchase #5 $249.35   3.452%   $257.9576   $257.96   $257.95   $258.00  
  Purchase #6 $168.61   11.397%   $187.8265   $187.83   $187.85   $187.80  
  Purchase #7 $206.38   11.571%   $230.2602   $230.26   $230.25   $230.30  
  7 purchase totals = $1,146.52       $1,254.6182   $1,254.62   $1,254.60   $1,254.60