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 $152.92   9.546%   $167.5177   $167.52   $167.50   $167.50  
  Purchase #2 $91.83   7.394%   $98.6199   $98.62   $98.60   $98.60  
  Purchase #3 $198.88   4.182%   $207.1972   $207.20   $207.20   $207.20  
  Purchase #4 $58.65   11.866%   $65.6094   $65.61   $65.60   $65.60  
  Purchase #5 $99.61   9.696%   $109.2682   $109.27   $109.25   $109.30  
  Purchase #6 $13.66   11.232%   $15.1943   $15.19   $15.20   $15.20  
  Purchase #7 $179.59   11.525%   $200.2877   $200.29   $200.30   $200.30  
  7 purchase totals = $795.14       $863.6944   $863.70   $863.65   $863.70