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 $203.27   11.557%   $226.7619   $226.76   $226.75   $226.80  
  Purchase #2 $229.33   8.284%   $248.3277   $248.33   $248.35   $248.30  
  Purchase #3 $187.48   5.331%   $197.4746   $197.47   $197.45   $197.50  
  Purchase #4 $107.99   12.169%   $121.1313   $121.13   $121.15   $121.10  
  Purchase #5 $178.59   9.305%   $195.2078   $195.21   $195.20   $195.20  
  Purchase #6 $174.51   13.529%   $198.1195   $198.12   $198.10   $198.10  
  Purchase #7 $80.78   3.492%   $83.6008   $83.60   $83.60   $83.60  
  7 purchase totals = $1,161.95       $1,270.6236   $1,270.62   $1,270.60   $1,270.60