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 $209.80   11.730%   $234.4095   $234.41   $234.40   $234.40  
  Purchase #2 $134.75   6.702%   $143.7809   $143.78   $143.80   $143.80  
  Purchase #3 $59.63   10.687%   $66.0027   $66.00   $66.00   $66.00  
  Purchase #4 $196.62   5.589%   $207.6091   $207.61   $207.60   $207.60  
  Purchase #5 $146.49   7.578%   $157.591   $157.59   $157.60   $157.60  
  Purchase #6 $105.39   9.865%   $115.7867   $115.79   $115.80   $115.80  
  Purchase #7 $110.50   13.677%   $125.6131   $125.61   $125.60   $125.60  
  7 purchase totals = $963.18       $1,050.7930   $1,050.79   $1,050.80   $1,050.80