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 $71.79   5.805%   $75.9574   $75.96   $75.95   $76.00  
  Purchase #2 $131.63   6.335%   $139.9688   $139.97   $139.95   $140.00  
  Purchase #3 $202.99   12.149%   $227.6513   $227.65   $227.65   $227.70  
  Purchase #4 $145.58   9.697%   $159.6969   $159.70   $159.70   $159.70  
  Purchase #5 $167.76   7.334%   $180.0635   $180.06   $180.05   $180.10  
  Purchase #6 $206.28   12.606%   $232.2837   $232.28   $232.30   $232.30  
  Purchase #7 $204.93   11.471%   $228.4375   $228.44   $228.45   $228.40  
  7 purchase totals = $1,130.96       $1,244.0591   $1,244.06   $1,244.05   $1,244.20