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 $142.98   7.531%   $153.7478   $153.75   $153.75   $153.70  
  Purchase #2 $8.62   13.647%   $9.7964   $9.80   $9.80   $9.80  
  Purchase #3 $162.90   6.363%   $173.2653   $173.27   $173.25   $173.30  
  Purchase #4 $61.49   5.500%   $64.872   $64.87   $64.85   $64.90  
  Purchase #5 $198.62   4.480%   $207.5182   $207.52   $207.50   $207.50  
  Purchase #6 $152.74   8.271%   $165.3731   $165.37   $165.35   $165.40  
  Purchase #7 $24.37   4.106%   $25.3706   $25.37   $25.35   $25.40  
  7 purchase totals = $751.72       $799.9434   $799.95   $799.85   $800.00