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 $48.45   3.129%   $49.966   $49.97   $49.95   $50.00  
  Purchase #2 $214.48   13.663%   $243.7844   $243.78   $243.80   $243.80  
  Purchase #3 $64.92   10.480%   $71.7236   $71.72   $71.70   $71.70  
  Purchase #4 $53.76   9.535%   $58.886   $58.89   $58.90   $58.90  
  Purchase #5 $182.34   9.118%   $198.9658   $198.97   $198.95   $199.00  
  Purchase #6 $113.98   4.292%   $118.872   $118.87   $118.85   $118.90  
  Purchase #7 $147.31   13.644%   $167.409   $167.41   $167.40   $167.40  
  7 purchase totals = $825.24       $909.6068   $909.61   $909.55   $909.70