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 $171.75   13.352%   $194.6821   $194.68   $194.70   $194.70  
  Purchase #2 $14.83   13.692%   $16.8605   $16.86   $16.85   $16.90  
  Purchase #3 $54.41   13.392%   $61.6966   $61.70   $61.70   $61.70  
  Purchase #4 $61.82   8.206%   $66.8929   $66.89   $66.90   $66.90  
  Purchase #5 $238.29   8.115%   $257.6272   $257.63   $257.65   $257.60  
  Purchase #6 $162.43   8.852%   $176.8083   $176.81   $176.80   $176.80  
  Purchase #7 $157.97   11.192%   $175.65   $175.65   $175.65   $175.70  
  7 purchase totals = $861.50       $950.2176   $950.22   $950.25   $950.30