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 $165.61   8.544%   $179.7597   $179.76   $179.75   $179.80  
  Purchase #2 $77.81   8.330%   $84.2916   $84.29   $84.30   $84.30  
  Purchase #3 $222.98   4.180%   $232.3006   $232.30   $232.30   $232.30  
  Purchase #4 $51.30   12.514%   $57.7197   $57.72   $57.70   $57.70  
  Purchase #5 $240.91   11.454%   $268.5038   $268.50   $268.50   $268.50  
  Purchase #6 $181.27   11.327%   $201.8025   $201.80   $201.80   $201.80  
  Purchase #7 $247.40   9.633%   $271.232   $271.23   $271.25   $271.20  
  7 purchase totals = $1,187.28       $1,295.6099   $1,295.60   $1,295.60   $1,295.60