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 $84.96   12.148%   $95.2809   $95.28   $95.30   $95.30  
  Purchase #2 $58.55   11.734%   $65.4203   $65.42   $65.40   $65.40  
  Purchase #3 $23.91   13.765%   $27.2012   $27.20   $27.20   $27.20  
  Purchase #4 $71.28   8.874%   $77.6054   $77.61   $77.60   $77.60  
  Purchase #5 $179.72   4.384%   $187.5989   $187.60   $187.60   $187.60  
  Purchase #6 $243.38   5.617%   $257.0507   $257.05   $257.05   $257.10  
  Purchase #7 $158.48   4.223%   $165.1726   $165.17   $165.15   $165.20  
  7 purchase totals = $820.28       $875.3300   $875.33   $875.30   $875.40