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 $85.46   8.819%   $92.9967   $93.00   $93.00   $93.00  
  Purchase #2 $248.80   12.384%   $279.6114   $279.61   $279.60   $279.60  
  Purchase #3 $188.82   7.412%   $202.8153   $202.82   $202.80   $202.80  
  Purchase #4 $130.41   11.364%   $145.2298   $145.23   $145.25   $145.20  
  Purchase #5 $14.86   11.692%   $16.5974   $16.60   $16.60   $16.60  
  Purchase #6 $138.62   9.382%   $151.6253   $151.63   $151.65   $151.60  
  Purchase #7 $55.41   10.622%   $61.2957   $61.30   $61.30   $61.30  
  7 purchase totals = $862.38       $950.1716   $950.19   $950.20   $950.10