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 $193.89   3.823%   $201.3024   $201.30   $201.30   $201.30  
  Purchase #2 $225.27   12.386%   $253.1719   $253.17   $253.15   $253.20  
  Purchase #3 $218.69   9.543%   $239.5596   $239.56   $239.55   $239.60  
  Purchase #4 $19.73   9.365%   $21.5777   $21.58   $21.60   $21.60  
  Purchase #5 $42.93   8.802%   $46.7087   $46.71   $46.70   $46.70  
  Purchase #6 $197.75   7.156%   $211.901   $211.90   $211.90   $211.90  
  Purchase #7 $94.68   7.736%   $102.0044   $102.00   $102.00   $102.00  
  7 purchase totals = $992.94       $1,076.2257   $1,076.22   $1,076.20   $1,076.30