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 $53.98   11.246%   $60.0506   $60.05   $60.05   $60.10  
  Purchase #2 $241.74   3.257%   $249.6135   $249.61   $249.60   $249.60  
  Purchase #3 $116.94   12.207%   $131.2149   $131.21   $131.20   $131.20  
  Purchase #4 $94.93   8.505%   $103.0038   $103.00   $103.00   $103.00  
  Purchase #5 $188.89   10.193%   $208.1436   $208.14   $208.15   $208.10  
  Purchase #6 $204.32   9.122%   $222.9581   $222.96   $222.95   $223.00  
  Purchase #7 $37.35   5.570%   $39.4304   $39.43   $39.45   $39.40  
  7 purchase totals = $938.15       $1,014.4149   $1,014.40   $1,014.40   $1,014.40