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 $236.72   13.200%   $267.967   $267.97   $267.95   $268.00  
  Purchase #2 $141.68   11.501%   $157.9746   $157.97   $157.95   $158.00  
  Purchase #3 $230.35   8.567%   $250.0841   $250.08   $250.10   $250.10  
  Purchase #4 $231.35   4.528%   $241.8255   $241.83   $241.85   $241.80  
  Purchase #5 $55.69   8.612%   $60.486   $60.49   $60.50   $60.50  
  Purchase #6 $211.73   6.414%   $225.3104   $225.31   $225.30   $225.30  
  Purchase #7 $196.46   6.850%   $209.9175   $209.92   $209.90   $209.90  
  7 purchase totals = $1,303.98       $1,413.5651   $1,413.57   $1,413.55   $1,413.60