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 $66.99   7.424%   $71.9633   $71.96   $71.95   $72.00  
  Purchase #2 $13.27   6.132%   $14.0837   $14.08   $14.10   $14.10  
  Purchase #3 $101.78   3.764%   $105.611   $105.61   $105.60   $105.60  
  Purchase #4 $28.64   11.523%   $31.9402   $31.94   $31.95   $31.90  
  Purchase #5 $13.60   13.676%   $15.4599   $15.46   $15.45   $15.50  
  Purchase #6 $174.66   9.528%   $191.3016   $191.30   $191.30   $191.30  
  Purchase #7 $156.81   8.775%   $170.5701   $170.57   $170.55   $170.60  
  7 purchase totals = $555.75       $600.9298   $600.92   $600.90   $601.00