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 $182.88   12.370%   $205.5023   $205.50   $205.50   $205.50  
  Purchase #2 $62.87   8.532%   $68.2341   $68.23   $68.25   $68.20  
  Purchase #3 $69.44   6.161%   $73.7182   $73.72   $73.70   $73.70  
  Purchase #4 $146.52   11.122%   $162.816   $162.82   $162.80   $162.80  
  Purchase #5 $167.88   8.678%   $182.4486   $182.45   $182.45   $182.40  
  Purchase #6 $139.99   10.722%   $154.9997   $155.00   $155.00   $155.00  
  Purchase #7 $91.31   5.422%   $96.2608   $96.26   $96.25   $96.30  
  7 purchase totals = $860.89       $943.9797   $943.98   $943.95   $943.90