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 $191.87   8.494%   $208.1674   $208.17   $208.15   $208.20  
  Purchase #2 $25.66   10.420%   $28.3338   $28.33   $28.35   $28.30  
  Purchase #3 $119.54   6.787%   $127.6532   $127.65   $127.65   $127.70  
  Purchase #4 $174.73   11.767%   $195.2905   $195.29   $195.30   $195.30  
  Purchase #5 $10.98   4.271%   $11.449   $11.45   $11.45   $11.40  
  Purchase #6 $230.70   12.474%   $259.4775   $259.48   $259.50   $259.50  
  Purchase #7 $154.66   9.801%   $169.8182   $169.82   $169.80   $169.80  
  7 purchase totals = $908.14       $1,000.1896   $1,000.19   $1,000.20   $1,000.20