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 $65.69   13.203%   $74.3631   $74.36   $74.35   $74.40  
  Purchase #2 $236.99   6.439%   $252.2498   $252.25   $252.25   $252.20  
  Purchase #3 $44.49   12.454%   $50.0308   $50.03   $50.05   $50.00  
  Purchase #4 $180.87   11.542%   $201.746   $201.75   $201.75   $201.70  
  Purchase #5 $58.79   11.636%   $65.6308   $65.63   $65.65   $65.60  
  Purchase #6 $86.30   9.758%   $94.7212   $94.72   $94.70   $94.70  
  Purchase #7 $218.51   9.664%   $239.6268   $239.63   $239.65   $239.60  
  7 purchase totals = $891.64       $978.3685   $978.37   $978.40   $978.20