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 $208.86   11.457%   $232.7891   $232.79   $232.80   $232.80  
  Purchase #2 $78.95   6.332%   $83.9491   $83.95   $83.95   $83.90  
  Purchase #3 $20.86   12.629%   $23.4944   $23.49   $23.50   $23.50  
  Purchase #4 $121.27   7.204%   $130.0063   $130.01   $130.00   $130.00  
  Purchase #5 $206.32   13.202%   $233.5584   $233.56   $233.55   $233.60  
  Purchase #6 $11.43   5.440%   $12.0518   $12.05   $12.05   $12.10  
  Purchase #7 $38.93   13.487%   $44.1805   $44.18   $44.20   $44.20  
  7 purchase totals = $686.62       $760.0296   $760.03   $760.05   $760.10