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 $244.37   11.726%   $273.0248   $273.02   $273.00   $273.00  
  Purchase #2 $162.94   5.397%   $171.7339   $171.73   $171.75   $171.70  
  Purchase #3 $33.42   5.704%   $35.3263   $35.33   $35.35   $35.30  
  Purchase #4 $203.80   7.345%   $218.7691   $218.77   $218.75   $218.80  
  Purchase #5 $219.42   11.362%   $244.3505   $244.35   $244.35   $244.40  
  Purchase #6 $116.27   3.608%   $120.465   $120.47   $120.45   $120.50  
  Purchase #7 $219.44   11.338%   $244.3201   $244.32   $244.30   $244.30  
  7 purchase totals = $1,199.66       $1,307.9897   $1,307.99   $1,307.95   $1,308.00