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 $116.75   8.429%   $126.5909   $126.59   $126.60   $126.60  
  Purchase #2 $104.47   7.167%   $111.9574   $111.96   $111.95   $112.00  
  Purchase #3 $20.65   13.305%   $23.3975   $23.40   $23.40   $23.40  
  Purchase #4 $163.56   6.387%   $174.0066   $174.01   $174.00   $174.00  
  Purchase #5 $213.92   5.157%   $224.9519   $224.95   $224.95   $225.00  
  Purchase #6 $178.44   4.419%   $186.3253   $186.33   $186.35   $186.30  
  Purchase #7 $192.80   4.228%   $200.9516   $200.95   $200.95   $201.00  
  7 purchase totals = $990.59       $1,048.1812   $1,048.19   $1,048.20   $1,048.30