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 $193.87   6.344%   $206.1691   $206.17   $206.15   $206.20  
  Purchase #2 $211.41   6.391%   $224.9212   $224.92   $224.90   $224.90  
  Purchase #3 $58.33   7.517%   $62.7147   $62.71   $62.70   $62.70  
  Purchase #4 $161.51   10.870%   $179.0661   $179.07   $179.05   $179.10  
  Purchase #5 $14.45   12.276%   $16.2239   $16.22   $16.20   $16.20  
  Purchase #6 $96.83   10.662%   $107.154   $107.15   $107.15   $107.20  
  Purchase #7 $218.91   3.550%   $226.6813   $226.68   $226.70   $226.70  
  7 purchase totals = $955.31       $1,022.9303   $1,022.92   $1,022.85   $1,023.00