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 $64.66   4.796%   $67.7611   $67.76   $67.75   $67.80  
  Purchase #2 $5.28   7.620%   $5.6823   $5.68   $5.70   $5.70  
  Purchase #3 $147.43   4.394%   $153.9081   $153.91   $153.90   $153.90  
  Purchase #4 $150.70   3.205%   $155.5299   $155.53   $155.55   $155.50  
  Purchase #5 $138.42   10.535%   $153.0025   $153.00   $153.00   $153.00  
  Purchase #6 $250.26   10.575%   $276.725   $276.73   $276.75   $276.70  
  Purchase #7 $219.41   6.496%   $233.6629   $233.66   $233.65   $233.70  
  7 purchase totals = $976.16       $1,046.2718   $1,046.27   $1,046.30   $1,046.30