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 $94.34   8.841%   $102.6806   $102.68   $102.70   $102.70  
  Purchase #2 $166.96   11.190%   $185.6428   $185.64   $185.65   $185.60  
  Purchase #3 $22.82   8.760%   $24.819   $24.82   $24.80   $24.80  
  Purchase #4 $44.97   12.497%   $50.5899   $50.59   $50.60   $50.60  
  Purchase #5 $165.90   11.155%   $184.4061   $184.41   $184.40   $184.40  
  Purchase #6 $188.40   5.667%   $199.0766   $199.08   $199.10   $199.10  
  Purchase #7 $123.57   10.380%   $136.3966   $136.40   $136.40   $136.40  
  7 purchase totals = $806.96       $883.6116   $883.62   $883.65   $883.60