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 $20.48   8.736%   $22.2691   $22.27   $22.25   $22.30  
  Purchase #2 $5.40   5.796%   $5.713   $5.71   $5.70   $5.70  
  Purchase #3 $196.74   5.402%   $207.3679   $207.37   $207.35   $207.40  
  Purchase #4 $79.41   4.122%   $82.6833   $82.68   $82.70   $82.70  
  Purchase #5 $81.36   7.393%   $87.3749   $87.37   $87.35   $87.40  
  Purchase #6 $89.30   7.320%   $95.8368   $95.84   $95.85   $95.80  
  Purchase #7 $243.63   10.606%   $269.4694   $269.47   $269.45   $269.50  
  7 purchase totals = $716.32       $770.7144   $770.71   $770.65   $770.80