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 $90.71   5.135%   $95.368   $95.37   $95.35   $95.40  
  Purchase #2 $205.31   13.527%   $233.0823   $233.08   $233.10   $233.10  
  Purchase #3 $186.93   5.613%   $197.4224   $197.42   $197.40   $197.40  
  Purchase #4 $137.58   4.657%   $143.9871   $143.99   $144.00   $144.00  
  Purchase #5 $122.42   11.400%   $136.3759   $136.38   $136.40   $136.40  
  Purchase #6 $103.29   13.114%   $116.8355   $116.84   $116.85   $116.80  
  Purchase #7 $90.63   11.344%   $100.9111   $100.91   $100.90   $100.90  
  7 purchase totals = $936.87       $1,023.9823   $1,023.99   $1,024.00   $1,024.00