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 $57.68   8.557%   $62.6157   $62.62   $62.60   $62.60  
  Purchase #2 $190.97   13.249%   $216.2716   $216.27   $216.25   $216.30  
  Purchase #3 $64.60   9.843%   $70.9586   $70.96   $70.95   $71.00  
  Purchase #4 $38.58   5.862%   $40.8416   $40.84   $40.85   $40.80  
  Purchase #5 $216.94   5.858%   $229.6483   $229.65   $229.65   $229.60  
  Purchase #6 $192.54   7.591%   $207.1557   $207.16   $207.15   $207.20  
  Purchase #7 $15.78   12.261%   $17.7148   $17.71   $17.70   $17.70  
  7 purchase totals = $777.09       $845.2063   $845.21   $845.15   $845.20