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 $244.63   7.589%   $263.195   $263.20   $263.20   $263.20  
  Purchase #2 $65.93   3.417%   $68.1828   $68.18   $68.20   $68.20  
  Purchase #3 $106.52   7.449%   $114.4547   $114.45   $114.45   $114.50  
  Purchase #4 $156.47   12.240%   $175.6219   $175.62   $175.60   $175.60  
  Purchase #5 $216.25   3.840%   $224.554   $224.55   $224.55   $224.60  
  Purchase #6 $174.68   4.139%   $181.91   $181.91   $181.90   $181.90  
  Purchase #7 $181.35   7.681%   $195.2795   $195.28   $195.30   $195.30  
  7 purchase totals = $1,145.83       $1,223.1979   $1,223.19   $1,223.20   $1,223.30