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 $224.38   9.740%   $246.2346   $246.23   $246.25   $246.20  
  Purchase #2 $163.93   9.367%   $179.2853   $179.29   $179.30   $179.30  
  Purchase #3 $157.47   13.810%   $179.2166   $179.22   $179.20   $179.20  
  Purchase #4 $223.57   5.494%   $235.8529   $235.85   $235.85   $235.90  
  Purchase #5 $144.74   8.173%   $156.5696   $156.57   $156.55   $156.60  
  Purchase #6 $213.41   9.589%   $233.8739   $233.87   $233.85   $233.90  
  Purchase #7 $166.85   9.577%   $182.8292   $182.83   $182.85   $182.80  
  7 purchase totals = $1,294.35       $1,413.8621   $1,413.86   $1,413.85   $1,413.90