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 $38.83   11.614%   $43.3397   $43.34   $43.35   $43.30  
  Purchase #2 $31.72   9.260%   $34.6573   $34.66   $34.65   $34.70  
  Purchase #3 $249.96   12.472%   $281.135   $281.14   $281.15   $281.10  
  Purchase #4 $188.87   8.426%   $204.7842   $204.78   $204.80   $204.80  
  Purchase #5 $118.49   4.619%   $123.9631   $123.96   $123.95   $124.00  
  Purchase #6 $103.51   4.731%   $108.4071   $108.41   $108.40   $108.40  
  Purchase #7 $239.25   8.286%   $259.0743   $259.07   $259.05   $259.10  
  7 purchase totals = $970.63       $1,055.3607   $1,055.36   $1,055.35   $1,055.40