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 $208.72   11.620%   $232.9733   $232.97   $232.95   $233.00  
  Purchase #2 $125.59   12.515%   $141.3076   $141.31   $141.30   $141.30  
  Purchase #3 $23.57   6.540%   $25.1115   $25.11   $25.10   $25.10  
  Purchase #4 $222.33   12.729%   $250.6304   $250.63   $250.65   $250.60  
  Purchase #5 $143.61   3.284%   $148.3262   $148.33   $148.35   $148.30  
  Purchase #6 $11.61   3.544%   $12.0215   $12.02   $12.00   $12.00  
  Purchase #7 $47.62   6.132%   $50.5401   $50.54   $50.55   $50.50  
  7 purchase totals = $783.05       $860.9106   $860.91   $860.90   $860.80