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 $69.69   10.563%   $77.0514   $77.05   $77.05   $77.10  
  Purchase #2 $238.86   11.377%   $266.0351   $266.04   $266.05   $266.00  
  Purchase #3 $224.59   12.684%   $253.077   $253.08   $253.10   $253.10  
  Purchase #4 $100.99   11.843%   $112.9502   $112.95   $112.95   $113.00  
  Purchase #5 $85.31   7.357%   $91.5863   $91.59   $91.60   $91.60  
  Purchase #6 $196.50   13.522%   $223.0707   $223.07   $223.05   $223.10  
  Purchase #7 $200.47   13.142%   $226.8158   $226.82   $226.80   $226.80  
  7 purchase totals = $1,116.41       $1,250.5865   $1,250.60   $1,250.60   $1,250.70