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 $155.32   6.541%   $165.4795   $165.48   $165.50   $165.50  
  Purchase #2 $246.41   5.495%   $259.9502   $259.95   $259.95   $260.00  
  Purchase #3 $47.97   9.822%   $52.6816   $52.68   $52.70   $52.70  
  Purchase #4 $153.84   7.361%   $165.1642   $165.16   $165.15   $165.20  
  Purchase #5 $24.44   4.454%   $25.5286   $25.53   $25.55   $25.50  
  Purchase #6 $23.34   10.300%   $25.744   $25.74   $25.75   $25.70  
  Purchase #7 $16.34   5.574%   $17.2508   $17.25   $17.25   $17.30  
  7 purchase totals = $667.66       $711.7989   $711.79   $711.85   $711.90