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 $117.91   7.680%   $126.9655   $126.97   $126.95   $127.00  
  Purchase #2 $211.32   6.394%   $224.8318   $224.83   $224.85   $224.80  
  Purchase #3 $36.36   8.289%   $39.3739   $39.37   $39.35   $39.40  
  Purchase #4 $111.69   3.185%   $115.2473   $115.25   $115.25   $115.20  
  Purchase #5 $223.45   9.462%   $244.5928   $244.59   $244.60   $244.60  
  Purchase #6 $26.56   12.371%   $29.8457   $29.85   $29.85   $29.80  
  Purchase #7 $218.30   6.540%   $232.5768   $232.58   $232.60   $232.60  
  7 purchase totals = $945.59       $1,013.4338   $1,013.44   $1,013.45   $1,013.40