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 $23.63   3.713%   $24.5074   $24.51   $24.50   $24.50  
  Purchase #2 $210.69   12.202%   $236.3984   $236.40   $236.40   $236.40  
  Purchase #3 $137.59   11.423%   $153.3069   $153.31   $153.30   $153.30  
  Purchase #4 $65.30   13.808%   $74.3166   $74.32   $74.30   $74.30  
  Purchase #5 $173.63   11.607%   $193.7832   $193.78   $193.80   $193.80  
  Purchase #6 $110.72   12.227%   $124.2577   $124.26   $124.25   $124.30  
  Purchase #7 $200.90   5.543%   $212.0359   $212.04   $212.05   $212.00  
  7 purchase totals = $922.46       $1,018.6061   $1,018.62   $1,018.60   $1,018.60