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 $61.76   7.282%   $66.2574   $66.26   $66.25   $66.30  
  Purchase #2 $110.93   5.243%   $116.7461   $116.75   $116.75   $116.70  
  Purchase #3 $153.73   13.172%   $173.9793   $173.98   $174.00   $174.00  
  Purchase #4 $14.87   5.437%   $15.6785   $15.68   $15.70   $15.70  
  Purchase #5 $200.71   11.355%   $223.5006   $223.50   $223.50   $223.50  
  Purchase #6 $205.91   13.214%   $233.1189   $233.12   $233.10   $233.10  
  Purchase #7 $117.56   9.380%   $128.5871   $128.59   $128.60   $128.60  
  7 purchase totals = $865.47       $957.8679   $957.88   $957.90   $957.90