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 $201.61   13.339%   $228.5028   $228.50   $228.50   $228.50  
  Purchase #2 $133.84   12.217%   $150.1912   $150.19   $150.20   $150.20  
  Purchase #3 $101.90   12.692%   $114.8331   $114.83   $114.85   $114.80  
  Purchase #4 $204.84   10.287%   $225.9119   $225.91   $225.90   $225.90  
  Purchase #5 $118.28   13.434%   $134.1697   $134.17   $134.15   $134.20  
  Purchase #6 $44.86   3.433%   $46.4   $46.40   $46.40   $46.40  
  Purchase #7 $118.36   5.491%   $124.8591   $124.86   $124.85   $124.90  
  7 purchase totals = $923.69       $1,024.8678   $1,024.86   $1,024.85   $1,024.90