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 $61.39   7.562%   $66.0323   $66.03   $66.05   $66.00  
  Purchase #2 $194.51   12.563%   $218.9463   $218.95   $218.95   $218.90  
  Purchase #3 $217.94   3.330%   $225.1974   $225.20   $225.20   $225.20  
  Purchase #4 $196.46   3.874%   $204.0709   $204.07   $204.05   $204.10  
  Purchase #5 $192.54   9.559%   $210.9449   $210.94   $210.95   $210.90  
  Purchase #6 $172.96   5.249%   $182.0387   $182.04   $182.05   $182.00  
  Purchase #7 $248.97   5.149%   $261.7895   $261.79   $261.80   $261.80  
  7 purchase totals = $1,284.77       $1,369.0200   $1,369.02   $1,369.05   $1,368.90