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 $12.95   8.614%   $14.0655   $14.07   $14.05   $14.10  
  Purchase #2 $181.86   11.374%   $202.5448   $202.54   $202.55   $202.50  
  Purchase #3 $94.68   8.305%   $102.5432   $102.54   $102.55   $102.50  
  Purchase #4 $127.89   13.536%   $145.2012   $145.20   $145.20   $145.20  
  Purchase #5 $133.67   10.130%   $147.2108   $147.21   $147.20   $147.20  
  Purchase #6 $239.80   10.494%   $264.9646   $264.96   $264.95   $265.00  
  Purchase #7 $66.98   12.673%   $75.4684   $75.47   $75.45   $75.50  
  7 purchase totals = $857.83       $951.9985   $951.99   $951.95   $952.00