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 $119.99   3.476%   $124.1609   $124.16   $124.15   $124.20  
  Purchase #2 $140.26   3.121%   $144.6375   $144.64   $144.65   $144.60  
  Purchase #3 $184.54   3.547%   $191.0856   $191.09   $191.10   $191.10  
  Purchase #4 $242.34   8.706%   $263.4381   $263.44   $263.45   $263.40  
  Purchase #5 $218.93   3.701%   $227.0326   $227.03   $227.05   $227.00  
  Purchase #6 $11.74   3.576%   $12.1598   $12.16   $12.15   $12.20  
  Purchase #7 $203.75   4.398%   $212.7109   $212.71   $212.70   $212.70  
  7 purchase totals = $1,121.55       $1,175.2254   $1,175.23   $1,175.25   $1,175.20