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 $204.36   5.470%   $215.5385   $215.54   $215.55   $215.50  
  Purchase #2 $202.57   11.264%   $225.3875   $225.39   $225.40   $225.40  
  Purchase #3 $153.30   3.658%   $158.9077   $158.91   $158.90   $158.90  
  Purchase #4 $77.84   13.670%   $88.4807   $88.48   $88.50   $88.50  
  Purchase #5 $97.72   6.492%   $104.064   $104.06   $104.05   $104.10  
  Purchase #6 $237.97   5.372%   $250.7537   $250.75   $250.75   $250.80  
  Purchase #7 $15.69   6.106%   $16.648   $16.65   $16.65   $16.60  
  7 purchase totals = $989.45       $1,059.7801   $1,059.78   $1,059.80   $1,059.80