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 $235.65   8.575%   $255.857   $255.86   $255.85   $255.90  
  Purchase #2 $126.47   13.612%   $143.6851   $143.69   $143.70   $143.70  
  Purchase #3 $63.94   6.360%   $68.0066   $68.01   $68.00   $68.00  
  Purchase #4 $99.92   3.373%   $103.2903   $103.29   $103.30   $103.30  
  Purchase #5 $206.58   12.161%   $231.7022   $231.70   $231.70   $231.70  
  Purchase #6 $79.61   11.732%   $88.9498   $88.95   $88.95   $88.90  
  Purchase #7 $126.51   6.232%   $134.3941   $134.39   $134.40   $134.40  
  7 purchase totals = $938.68       $1,025.8851   $1,025.89   $1,025.90   $1,025.90