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 $243.48   11.694%   $271.9526   $271.95   $271.95   $272.00  
  Purchase #2 $91.28   4.766%   $95.6304   $95.63   $95.65   $95.60  
  Purchase #3 $31.49   4.157%   $32.799   $32.80   $32.80   $32.80  
  Purchase #4 $123.80   6.569%   $131.9324   $131.93   $131.95   $131.90  
  Purchase #5 $21.59   10.253%   $23.8036   $23.80   $23.80   $23.80  
  Purchase #6 $186.31   13.355%   $211.1917   $211.19   $211.20   $211.20  
  Purchase #7 $207.94   8.782%   $226.2013   $226.20   $226.20   $226.20  
  7 purchase totals = $905.89       $993.5110   $993.50   $993.55   $993.50