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 $109.89   11.271%   $122.2757   $122.28   $122.30   $122.30  
  Purchase #2 $62.79   4.771%   $65.7857   $65.79   $65.80   $65.80  
  Purchase #3 $139.33   12.779%   $157.135   $157.14   $157.15   $157.10  
  Purchase #4 $163.81   8.449%   $177.6503   $177.65   $177.65   $177.70  
  Purchase #5 $234.70   3.707%   $243.4003   $243.40   $243.40   $243.40  
  Purchase #6 $32.55   11.216%   $36.2008   $36.20   $36.20   $36.20  
  Purchase #7 $206.83   8.226%   $223.8438   $223.84   $223.85   $223.80  
  7 purchase totals = $949.90       $1,026.2916   $1,026.30   $1,026.35   $1,026.30