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 $65.44   12.607%   $73.69   $73.69   $73.70   $73.70  
  Purchase #2 $8.87   4.801%   $9.2958   $9.30   $9.30   $9.30  
  Purchase #3 $192.73   7.232%   $206.6682   $206.67   $206.65   $206.70  
  Purchase #4 $130.56   10.445%   $144.197   $144.20   $144.20   $144.20  
  Purchase #5 $140.90   4.619%   $147.4082   $147.41   $147.40   $147.40  
  Purchase #6 $42.45   13.862%   $48.3344   $48.33   $48.35   $48.30  
  Purchase #7 $171.54   5.633%   $181.2028   $181.20   $181.20   $181.20  
  7 purchase totals = $752.49       $810.7964   $810.80   $810.80   $810.80