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 $206.26   10.717%   $228.3649   $228.36   $228.35   $228.40  
  Purchase #2 $131.88   7.803%   $142.1706   $142.17   $142.15   $142.20  
  Purchase #3 $56.41   7.573%   $60.6819   $60.68   $60.70   $60.70  
  Purchase #4 $219.37   11.738%   $245.1197   $245.12   $245.10   $245.10  
  Purchase #5 $6.80   3.441%   $7.034   $7.03   $7.05   $7.00  
  Purchase #6 $245.95   3.376%   $254.2533   $254.25   $254.25   $254.30  
  Purchase #7 $168.58   10.136%   $185.6673   $185.67   $185.65   $185.70  
  7 purchase totals = $1,035.25       $1,123.2917   $1,123.28   $1,123.25   $1,123.40