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 $67.32   5.634%   $71.1128   $71.11   $71.10   $71.10  
  Purchase #2 $233.89   5.391%   $246.499   $246.50   $246.50   $246.50  
  Purchase #3 $107.38   13.639%   $122.0256   $122.03   $122.05   $122.00  
  Purchase #4 $139.89   7.852%   $150.8742   $150.87   $150.85   $150.90  
  Purchase #5 $69.30   6.368%   $73.713   $73.71   $73.70   $73.70  
  Purchase #6 $168.74   6.744%   $180.1198   $180.12   $180.10   $180.10  
  Purchase #7 $91.94   3.304%   $94.9777   $94.98   $95.00   $95.00  
  7 purchase totals = $878.46       $939.3221   $939.32   $939.30   $939.30