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 $82.83   12.823%   $93.4513   $93.45   $93.45   $93.50  
  Purchase #2 $90.87   8.817%   $98.882   $98.88   $98.90   $98.90  
  Purchase #3 $137.81   11.804%   $154.0771   $154.08   $154.10   $154.10  
  Purchase #4 $208.31   4.388%   $217.4506   $217.45   $217.45   $217.50  
  Purchase #5 $146.80   7.405%   $157.6705   $157.67   $157.65   $157.70  
  Purchase #6 $132.68   13.395%   $150.4525   $150.45   $150.45   $150.50  
  Purchase #7 $205.49   6.257%   $218.3475   $218.35   $218.35   $218.30  
  7 purchase totals = $1,004.79       $1,090.3315   $1,090.33   $1,090.35   $1,090.50