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 $215.73   8.765%   $234.6387   $234.64   $234.65   $234.60  
  Purchase #2 $76.51   10.372%   $84.4456   $84.45   $84.45   $84.40  
  Purchase #3 $60.33   4.164%   $62.8421   $62.84   $62.85   $62.80  
  Purchase #4 $74.85   12.816%   $84.4428   $84.44   $84.45   $84.40  
  Purchase #5 $91.96   4.553%   $96.1469   $96.15   $96.15   $96.10  
  Purchase #6 $46.97   10.787%   $52.0367   $52.04   $52.05   $52.00  
  Purchase #7 $130.92   11.392%   $145.8344   $145.83   $145.85   $145.80  
  7 purchase totals = $697.27       $760.3872   $760.39   $760.45   $760.10