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 $144.29   3.761%   $149.7167   $149.72   $149.70   $149.70  
  Purchase #2 $190.25   6.644%   $202.8902   $202.89   $202.90   $202.90  
  Purchase #3 $58.78   9.723%   $64.4952   $64.50   $64.50   $64.50  
  Purchase #4 $105.61   10.411%   $116.6051   $116.61   $116.60   $116.60  
  Purchase #5 $157.45   5.427%   $165.9948   $165.99   $166.00   $166.00  
  Purchase #6 $221.76   12.839%   $250.2318   $250.23   $250.25   $250.20  
  Purchase #7 $241.55   7.743%   $260.2532   $260.25   $260.25   $260.30  
  7 purchase totals = $1,119.69       $1,210.1870   $1,210.19   $1,210.20   $1,210.20