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 $240.59   9.464%   $263.3594   $263.36   $263.35   $263.40  
  Purchase #2 $197.41   8.523%   $214.2353   $214.24   $214.25   $214.20  
  Purchase #3 $167.80   8.203%   $181.5646   $181.56   $181.55   $181.60  
  Purchase #4 $69.28   3.834%   $71.9362   $71.94   $71.95   $71.90  
  Purchase #5 $226.56   10.781%   $250.9854   $250.99   $251.00   $251.00  
  Purchase #6 $93.71   3.644%   $97.1248   $97.12   $97.10   $97.10  
  Purchase #7 $95.99   7.411%   $103.1038   $103.10   $103.10   $103.10  
  7 purchase totals = $1,091.34       $1,182.3095   $1,182.31   $1,182.30   $1,182.30