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 $168.85   8.871%   $183.8287   $183.83   $183.85   $183.80  
  Purchase #2 $106.66   11.622%   $119.056   $119.06   $119.05   $119.10  
  Purchase #3 $188.27   9.172%   $205.5381   $205.54   $205.55   $205.50  
  Purchase #4 $101.28   5.358%   $106.7066   $106.71   $106.70   $106.70  
  Purchase #5 $247.70   12.284%   $278.1275   $278.13   $278.15   $278.10  
  Purchase #6 $21.66   7.487%   $23.2817   $23.28   $23.30   $23.30  
  Purchase #7 $160.87   10.499%   $177.7597   $177.76   $177.75   $177.80  
  7 purchase totals = $995.29       $1,094.2983   $1,094.31   $1,094.35   $1,094.30