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 $5.31   4.384%   $5.5428   $5.54   $5.55   $5.50  
  Purchase #2 $19.74   5.350%   $20.7961   $20.80   $20.80   $20.80  
  Purchase #3 $193.58   6.719%   $206.5866   $206.59   $206.60   $206.60  
  Purchase #4 $247.39   5.254%   $260.3879   $260.39   $260.40   $260.40  
  Purchase #5 $10.31   4.403%   $10.7639   $10.76   $10.75   $10.80  
  Purchase #6 $238.47   4.376%   $248.9054   $248.91   $248.90   $248.90  
  Purchase #7 $230.95   5.379%   $243.3728   $243.37   $243.35   $243.40  
  7 purchase totals = $945.75       $996.3555   $996.36   $996.35   $996.40