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 $226.80   11.259%   $252.3354   $252.34   $252.35   $252.30  
  Purchase #2 $14.87   5.415%   $15.6752   $15.68   $15.70   $15.70  
  Purchase #3 $46.55   11.132%   $51.7319   $51.73   $51.75   $51.70  
  Purchase #4 $160.62   4.378%   $167.6519   $167.65   $167.65   $167.70  
  Purchase #5 $127.31   13.803%   $144.8826   $144.88   $144.90   $144.90  
  Purchase #6 $72.45   8.418%   $78.5488   $78.55   $78.55   $78.50  
  Purchase #7 $86.95   5.629%   $91.8444   $91.84   $91.85   $91.80  
  7 purchase totals = $735.55       $802.6702   $802.67   $802.75   $802.60