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 $243.83   9.580%   $267.1889   $267.19   $267.20   $267.20  
  Purchase #2 $57.83   7.781%   $62.3298   $62.33   $62.35   $62.30  
  Purchase #3 $108.34   9.760%   $118.914   $118.91   $118.90   $118.90  
  Purchase #4 $235.99   13.552%   $267.9714   $267.97   $267.95   $268.00  
  Purchase #5 $70.72   5.811%   $74.8295   $74.83   $74.85   $74.80  
  Purchase #6 $14.49   9.437%   $15.8574   $15.86   $15.85   $15.90  
  Purchase #7 $211.47   11.318%   $235.4042   $235.40   $235.40   $235.40  
  7 purchase totals = $942.67       $1,042.4952   $1,042.49   $1,042.50   $1,042.50