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 $85.71   8.153%   $92.6979   $92.70   $92.70   $92.70  
  Purchase #2 $95.67   7.339%   $102.6912   $102.69   $102.70   $102.70  
  Purchase #3 $197.78   5.172%   $208.0092   $208.01   $208.00   $208.00  
  Purchase #4 $134.35   9.219%   $146.7357   $146.74   $146.75   $146.70  
  Purchase #5 $178.58   13.116%   $202.0026   $202.00   $202.00   $202.00  
  Purchase #6 $224.45   8.321%   $243.1265   $243.13   $243.15   $243.10  
  Purchase #7 $74.80   5.428%   $78.8601   $78.86   $78.85   $78.90  
  7 purchase totals = $991.34       $1,074.1232   $1,074.13   $1,074.15   $1,074.10