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 $211.75   10.656%   $234.3141   $234.31   $234.30   $234.30  
  Purchase #2 $167.73   13.172%   $189.8234   $189.82   $189.80   $189.80  
  Purchase #3 $165.43   12.287%   $185.7564   $185.76   $185.75   $185.80  
  Purchase #4 $14.25   6.633%   $15.1952   $15.20   $15.20   $15.20  
  Purchase #5 $73.74   10.773%   $81.684   $81.68   $81.70   $81.70  
  Purchase #6 $48.27   6.833%   $51.5683   $51.57   $51.55   $51.60  
  Purchase #7 $231.68   4.554%   $242.2307   $242.23   $242.25   $242.20  
  7 purchase totals = $912.85       $1,000.5721   $1,000.57   $1,000.55   $1,000.60