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 $208.39   12.306%   $234.0345   $234.03   $234.05   $234.00  
  Purchase #2 $187.57   11.772%   $209.6507   $209.65   $209.65   $209.70  
  Purchase #3 $62.87   4.540%   $65.7243   $65.72   $65.70   $65.70  
  Purchase #4 $111.50   8.126%   $120.5605   $120.56   $120.55   $120.60  
  Purchase #5 $96.66   8.658%   $105.0288   $105.03   $105.05   $105.00  
  Purchase #6 $236.49   4.615%   $247.404   $247.40   $247.40   $247.40  
  Purchase #7 $34.43   5.790%   $36.4235   $36.42   $36.40   $36.40  
  7 purchase totals = $937.91       $1,018.8263   $1,018.81   $1,018.80   $1,018.80