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 $92.37   3.104%   $95.2372   $95.24   $95.25   $95.20  
  Purchase #2 $17.46   6.322%   $18.5638   $18.56   $18.55   $18.60  
  Purchase #3 $110.70   12.871%   $124.9482   $124.95   $124.95   $124.90  
  Purchase #4 $205.48   10.228%   $226.4965   $226.50   $226.50   $226.50  
  Purchase #5 $228.88   5.173%   $240.72   $240.72   $240.70   $240.70  
  Purchase #6 $118.65   13.174%   $134.281   $134.28   $134.30   $134.30  
  Purchase #7 $239.73   3.207%   $247.4181   $247.42   $247.40   $247.40  
  7 purchase totals = $1,013.27       $1,087.6648   $1,087.67   $1,087.65   $1,087.60