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 $76.47   8.592%   $83.0403   $83.04   $83.05   $83.00  
  Purchase #2 $217.26   9.480%   $237.8562   $237.86   $237.85   $237.90  
  Purchase #3 $241.37   3.545%   $249.9266   $249.93   $249.95   $249.90  
  Purchase #4 $65.29   6.115%   $69.2825   $69.28   $69.30   $69.30  
  Purchase #5 $249.49   7.244%   $267.5631   $267.56   $267.55   $267.60  
  Purchase #6 $218.56   11.167%   $242.9666   $242.97   $242.95   $243.00  
  Purchase #7 $241.36   11.731%   $269.6739   $269.67   $269.65   $269.70  
  7 purchase totals = $1,309.80       $1,420.3092   $1,420.31   $1,420.30   $1,420.40