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 $57.92   12.286%   $65.0361   $65.04   $65.05   $65.00  
  Purchase #2 $86.68   10.207%   $95.5274   $95.53   $95.55   $95.50  
  Purchase #3 $92.80   11.259%   $103.2484   $103.25   $103.25   $103.20  
  Purchase #4 $26.74   11.271%   $29.7539   $29.75   $29.75   $29.80  
  Purchase #5 $10.63   9.829%   $11.6748   $11.67   $11.65   $11.70  
  Purchase #6 $85.29   5.716%   $90.1652   $90.17   $90.15   $90.20  
  Purchase #7 $165.78   3.663%   $171.8525   $171.85   $171.85   $171.90  
  7 purchase totals = $525.84       $567.2583   $567.26   $567.25   $567.30