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 $42.91   4.817%   $44.977   $44.98   $45.00   $45.00  
  Purchase #2 $194.34   3.376%   $200.9009   $200.90   $200.90   $200.90  
  Purchase #3 $78.27   7.776%   $84.3563   $84.36   $84.35   $84.40  
  Purchase #4 $174.37   6.695%   $186.0441   $186.04   $186.05   $186.00  
  Purchase #5 $146.79   5.280%   $154.5405   $154.54   $154.55   $154.50  
  Purchase #6 $115.75   10.301%   $127.6734   $127.67   $127.65   $127.70  
  Purchase #7 $189.87   10.779%   $210.3361   $210.34   $210.35   $210.30  
  7 purchase totals = $942.30       $1,008.8283   $1,008.83   $1,008.85   $1,008.80