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 $212.87   10.711%   $235.6705   $235.67   $235.65   $235.70  
  Purchase #2 $161.39   7.473%   $173.4507   $173.45   $173.45   $173.50  
  Purchase #3 $167.49   11.257%   $186.3443   $186.34   $186.35   $186.30  
  Purchase #4 $118.82   12.687%   $133.8947   $133.89   $133.90   $133.90  
  Purchase #5 $212.65   3.863%   $220.8647   $220.86   $220.85   $220.90  
  Purchase #6 $76.30   12.365%   $85.7345   $85.73   $85.75   $85.70  
  Purchase #7 $9.51   4.641%   $9.9514   $9.95   $9.95   $10.00  
  7 purchase totals = $959.03       $1,045.9108   $1,045.89   $1,045.90   $1,046.00