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 $211.65   5.588%   $223.477   $223.48   $223.50   $223.50  
  Purchase #2 $51.25   8.799%   $55.7595   $55.76   $55.75   $55.80  
  Purchase #3 $65.49   3.788%   $67.9708   $67.97   $67.95   $68.00  
  Purchase #4 $79.91   10.184%   $88.048   $88.05   $88.05   $88.00  
  Purchase #5 $235.37   4.678%   $246.3806   $246.38   $246.40   $246.40  
  Purchase #6 $60.73   7.810%   $65.473   $65.47   $65.45   $65.50  
  Purchase #7 $108.74   3.589%   $112.6427   $112.64   $112.65   $112.60  
  7 purchase totals = $813.14       $859.7516   $859.75   $859.75   $859.80