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 $210.56   13.648%   $239.2972   $239.30   $239.30   $239.30  
  Purchase #2 $213.25   13.331%   $241.6784   $241.68   $241.70   $241.70  
  Purchase #3 $89.96   6.691%   $95.9792   $95.98   $96.00   $96.00  
  Purchase #4 $240.67   5.642%   $254.2486   $254.25   $254.25   $254.20  
  Purchase #5 $112.54   13.587%   $127.8308   $127.83   $127.85   $127.80  
  Purchase #6 $244.91   5.555%   $258.5148   $258.51   $258.50   $258.50  
  Purchase #7 $51.26   9.607%   $56.1845   $56.18   $56.20   $56.20  
  7 purchase totals = $1,163.15       $1,273.7335   $1,273.73   $1,273.80   $1,273.70