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 $244.38   3.842%   $253.7691   $253.77   $253.75   $253.80  
  Purchase #2 $81.80   13.514%   $92.8545   $92.85   $92.85   $92.90  
  Purchase #3 $111.33   10.566%   $123.0931   $123.09   $123.10   $123.10  
  Purchase #4 $23.73   3.641%   $24.594   $24.59   $24.60   $24.60  
  Purchase #5 $159.71   3.758%   $165.7119   $165.71   $165.70   $165.70  
  Purchase #6 $179.89   12.396%   $202.1892   $202.19   $202.20   $202.20  
  Purchase #7 $186.84   11.703%   $208.7059   $208.71   $208.70   $208.70  
  7 purchase totals = $987.68       $1,070.9177   $1,070.91   $1,070.90   $1,071.00