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 $204.45   4.806%   $214.2759   $214.28   $214.30   $214.30  
  Purchase #2 $245.95   8.821%   $267.6452   $267.65   $267.65   $267.60  
  Purchase #3 $225.35   13.152%   $254.988   $254.99   $255.00   $255.00  
  Purchase #4 $39.55   3.557%   $40.9568   $40.96   $40.95   $41.00  
  Purchase #5 $85.40   13.840%   $97.2194   $97.22   $97.20   $97.20  
  Purchase #6 $129.40   11.326%   $144.0558   $144.06   $144.05   $144.10  
  Purchase #7 $124.94   5.177%   $131.4081   $131.41   $131.40   $131.40  
  7 purchase totals = $1,055.04       $1,150.5492   $1,150.57   $1,150.55   $1,150.60