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 $189.54   11.871%   $212.0403   $212.04   $212.05   $212.00  
  Purchase #2 $246.50   12.603%   $277.5664   $277.57   $277.55   $277.60  
  Purchase #3 $91.30   7.713%   $98.342   $98.34   $98.35   $98.30  
  Purchase #4 $34.61   11.660%   $38.6455   $38.65   $38.65   $38.60  
  Purchase #5 $144.51   6.257%   $153.552   $153.55   $153.55   $153.60  
  Purchase #6 $122.38   7.552%   $131.6221   $131.62   $131.60   $131.60  
  Purchase #7 $191.90   8.636%   $208.4725   $208.47   $208.45   $208.50  
  7 purchase totals = $1,020.74       $1,120.2408   $1,120.24   $1,120.20   $1,120.20