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 $57.95   12.367%   $65.1167   $65.12   $65.10   $65.10  
  Purchase #2 $231.64   6.139%   $245.8604   $245.86   $245.85   $245.90  
  Purchase #3 $166.35   11.213%   $185.0028   $185.00   $185.00   $185.00  
  Purchase #4 $27.87   10.227%   $30.7203   $30.72   $30.70   $30.70  
  Purchase #5 $70.61   6.450%   $75.1643   $75.16   $75.15   $75.20  
  Purchase #6 $75.51   8.333%   $81.8022   $81.80   $81.80   $81.80  
  Purchase #7 $22.26   9.570%   $24.3903   $24.39   $24.40   $24.40  
  7 purchase totals = $652.19       $708.0570   $708.05   $708.00   $708.10