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 $51.73   13.745%   $58.8403   $58.84   $58.85   $58.80  
  Purchase #2 $173.25   7.468%   $186.1883   $186.19   $186.20   $186.20  
  Purchase #3 $113.92   7.493%   $122.456   $122.46   $122.45   $122.50  
  Purchase #4 $68.31   9.706%   $74.9402   $74.94   $74.95   $74.90  
  Purchase #5 $150.37   10.183%   $165.6822   $165.68   $165.70   $165.70  
  Purchase #6 $182.72   7.155%   $195.7936   $195.79   $195.80   $195.80  
  Purchase #7 $51.39   3.720%   $53.3017   $53.30   $53.30   $53.30  
  7 purchase totals = $791.69       $857.2023   $857.20   $857.25   $857.20