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 $241.75   10.287%   $266.6188   $266.62   $266.60   $266.60  
  Purchase #2 $58.97   11.764%   $65.9072   $65.91   $65.90   $65.90  
  Purchase #3 $232.97   7.774%   $251.0811   $251.08   $251.10   $251.10  
  Purchase #4 $170.56   13.705%   $193.9352   $193.94   $193.95   $193.90  
  Purchase #5 $185.63   10.213%   $204.5884   $204.59   $204.60   $204.60  
  Purchase #6 $53.69   10.642%   $59.4037   $59.40   $59.40   $59.40  
  Purchase #7 $67.58   6.525%   $71.9896   $71.99   $72.00   $72.00  
  7 purchase totals = $1,011.15       $1,113.5240   $1,113.53   $1,113.55   $1,113.50