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 $169.82   10.406%   $187.4915   $187.49   $187.50   $187.50  
  Purchase #2 $137.51   13.412%   $155.9528   $155.95   $155.95   $156.00  
  Purchase #3 $134.28   9.652%   $147.2407   $147.24   $147.25   $147.20  
  Purchase #4 $40.65   7.712%   $43.7849   $43.78   $43.80   $43.80  
  Purchase #5 $212.27   9.800%   $233.0725   $233.07   $233.05   $233.10  
  Purchase #6 $24.37   5.255%   $25.6506   $25.65   $25.65   $25.70  
  Purchase #7 $206.34   9.832%   $226.6273   $226.63   $226.65   $226.60  
  7 purchase totals = $925.24       $1,019.8203   $1,019.81   $1,019.85   $1,019.90