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 $116.81   6.124%   $123.9634   $123.96   $123.95   $124.00  
  Purchase #2 $188.41   7.829%   $203.1606   $203.16   $203.15   $203.20  
  Purchase #3 $40.65   10.432%   $44.8906   $44.89   $44.90   $44.90  
  Purchase #4 $122.96   7.734%   $132.4697   $132.47   $132.45   $132.50  
  Purchase #5 $130.72   11.445%   $145.6809   $145.68   $145.70   $145.70  
  Purchase #6 $34.81   8.688%   $37.8343   $37.83   $37.85   $37.80  
  Purchase #7 $69.47   12.171%   $77.9252   $77.93   $77.95   $77.90  
  7 purchase totals = $703.83       $765.9247   $765.92   $765.95   $766.00