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 $204.81   3.534%   $212.048   $212.05   $212.05   $212.00  
  Purchase #2 $152.98   3.260%   $157.9671   $157.97   $157.95   $158.00  
  Purchase #3 $25.43   5.657%   $26.8686   $26.87   $26.85   $26.90  
  Purchase #4 $95.68   12.611%   $107.7462   $107.75   $107.75   $107.70  
  Purchase #5 $64.79   11.629%   $72.3244   $72.32   $72.30   $72.30  
  Purchase #6 $5.70   11.718%   $6.3679   $6.37   $6.35   $6.40  
  Purchase #7 $116.86   10.134%   $128.7026   $128.70   $128.70   $128.70  
  7 purchase totals = $666.25       $712.0248   $712.03   $711.95   $712.00