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 $224.65   10.178%   $247.5149   $247.51   $247.50   $247.50  
  Purchase #2 $126.31   12.648%   $142.2857   $142.29   $142.30   $142.30  
  Purchase #3 $52.59   3.123%   $54.2324   $54.23   $54.25   $54.20  
  Purchase #4 $63.57   12.169%   $71.3058   $71.31   $71.30   $71.30  
  Purchase #5 $245.40   3.834%   $254.8086   $254.81   $254.80   $254.80  
  Purchase #6 $166.78   13.112%   $188.6482   $188.65   $188.65   $188.60  
  Purchase #7 $225.43   8.210%   $243.9378   $243.94   $243.95   $243.90  
  7 purchase totals = $1,104.73       $1,202.7334   $1,202.74   $1,202.75   $1,202.60