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 $193.53   5.486%   $204.1471   $204.15   $204.15   $204.10  
  Purchase #2 $18.87   10.138%   $20.783   $20.78   $20.80   $20.80  
  Purchase #3 $180.71   12.174%   $202.7096   $202.71   $202.70   $202.70  
  Purchase #4 $53.82   3.599%   $55.757   $55.76   $55.75   $55.80  
  Purchase #5 $94.73   6.602%   $100.9841   $100.98   $101.00   $101.00  
  Purchase #6 $55.43   8.754%   $60.2823   $60.28   $60.30   $60.30  
  Purchase #7 $53.41   5.459%   $56.3257   $56.33   $56.35   $56.30  
  7 purchase totals = $650.50       $700.9888   $700.99   $701.05   $701.00