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 $198.63   5.384%   $209.3242   $209.32   $209.30   $209.30  
  Purchase #2 $75.66   11.256%   $84.1763   $84.18   $84.20   $84.20  
  Purchase #3 $52.55   5.542%   $55.4623   $55.46   $55.45   $55.50  
  Purchase #4 $58.31   3.774%   $60.5106   $60.51   $60.50   $60.50  
  Purchase #5 $7.67   12.286%   $8.6123   $8.61   $8.60   $8.60  
  Purchase #6 $116.58   5.275%   $122.7296   $122.73   $122.75   $122.70  
  Purchase #7 $184.38   7.396%   $198.0167   $198.02   $198.00   $198.00  
  7 purchase totals = $693.78       $738.8320   $738.83   $738.80   $738.80