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 $93.57   3.456%   $96.8038   $96.80   $96.80   $96.80  
  Purchase #2 $242.48   5.357%   $255.4697   $255.47   $255.45   $255.50  
  Purchase #3 $14.43   9.183%   $15.7551   $15.76   $15.75   $15.80  
  Purchase #4 $132.84   11.387%   $147.9665   $147.97   $147.95   $148.00  
  Purchase #5 $66.35   6.407%   $70.601   $70.60   $70.60   $70.60  
  Purchase #6 $80.76   13.316%   $91.514   $91.51   $91.50   $91.50  
  Purchase #7 $109.44   5.529%   $115.4909   $115.49   $115.50   $115.50  
  7 purchase totals = $739.87       $793.6010   $793.60   $793.55   $793.70