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 $114.35   9.817%   $125.5757   $125.58   $125.60   $125.60  
  Purchase #2 $249.97   13.573%   $283.8984   $283.90   $283.90   $283.90  
  Purchase #3 $13.76   7.525%   $14.7954   $14.80   $14.80   $14.80  
  Purchase #4 $20.67   7.769%   $22.2759   $22.28   $22.30   $22.30  
  Purchase #5 $52.36   11.804%   $58.5406   $58.54   $58.55   $58.50  
  Purchase #6 $147.48   10.217%   $162.548   $162.55   $162.55   $162.50  
  Purchase #7 $204.58   9.183%   $223.3666   $223.37   $223.35   $223.40  
  7 purchase totals = $803.17       $891.0006   $891.02   $891.05   $891.00