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 $236.73   4.506%   $247.3971   $247.40   $247.40   $247.40  
  Purchase #2 $59.54   4.751%   $62.3687   $62.37   $62.35   $62.40  
  Purchase #3 $162.49   8.453%   $176.2253   $176.23   $176.25   $176.20  
  Purchase #4 $128.90   6.629%   $137.4448   $137.44   $137.45   $137.40  
  Purchase #5 $107.42   11.721%   $120.0107   $120.01   $120.00   $120.00  
  Purchase #6 $234.45   10.434%   $258.9125   $258.91   $258.90   $258.90  
  Purchase #7 $11.38   4.337%   $11.8736   $11.87   $11.85   $11.90  
  7 purchase totals = $940.91       $1,014.2327   $1,014.23   $1,014.20   $1,014.20