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 $218.96   8.398%   $237.3483   $237.35   $237.35   $237.30  
  Purchase #2 $205.73   10.417%   $227.1609   $227.16   $227.15   $227.20  
  Purchase #3 $95.30   3.394%   $98.5345   $98.53   $98.55   $98.50  
  Purchase #4 $40.53   7.232%   $43.4611   $43.46   $43.45   $43.50  
  Purchase #5 $75.45   12.292%   $84.7243   $84.72   $84.70   $84.70  
  Purchase #6 $93.59   4.444%   $97.7491   $97.75   $97.75   $97.70  
  Purchase #7 $201.83   6.238%   $214.4202   $214.42   $214.40   $214.40  
  7 purchase totals = $931.39       $1,003.3984   $1,003.39   $1,003.35   $1,003.30