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 $115.85   3.116%   $119.4599   $119.46   $119.45   $119.50  
  Purchase #2 $217.33   9.605%   $238.2045   $238.20   $238.20   $238.20  
  Purchase #3 $56.30   10.559%   $62.2447   $62.24   $62.25   $62.20  
  Purchase #4 $75.93   6.263%   $80.6855   $80.69   $80.70   $80.70  
  Purchase #5 $106.32   3.242%   $109.7669   $109.77   $109.75   $109.80  
  Purchase #6 $108.44   11.647%   $121.07   $121.07   $121.05   $121.10  
  Purchase #7 $55.45   13.576%   $62.9779   $62.98   $63.00   $63.00  
  7 purchase totals = $735.62       $794.4094   $794.41   $794.40   $794.50