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 $106.82   13.543%   $121.2866   $121.29   $121.30   $121.30  
  Purchase #2 $141.55   8.576%   $153.6893   $153.69   $153.70   $153.70  
  Purchase #3 $155.48   12.235%   $174.503   $174.50   $174.50   $174.50  
  Purchase #4 $238.31   13.785%   $271.161   $271.16   $271.15   $271.20  
  Purchase #5 $103.68   5.837%   $109.7318   $109.73   $109.75   $109.70  
  Purchase #6 $240.83   3.577%   $249.4445   $249.44   $249.45   $249.40  
  Purchase #7 $89.32   6.745%   $95.3446   $95.34   $95.35   $95.30  
  7 purchase totals = $1,075.99       $1,175.1608   $1,175.15   $1,175.20   $1,175.10