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 $247.60   5.390%   $260.9456   $260.95   $260.95   $260.90  
  Purchase #2 $17.26   5.531%   $18.2147   $18.21   $18.20   $18.20  
  Purchase #3 $17.93   8.656%   $19.482   $19.48   $19.50   $19.50  
  Purchase #4 $116.57   6.483%   $124.1272   $124.13   $124.15   $124.10  
  Purchase #5 $155.28   4.738%   $162.6372   $162.64   $162.65   $162.60  
  Purchase #6 $179.26   4.746%   $187.7677   $187.77   $187.75   $187.80  
  Purchase #7 $241.59   10.519%   $267.0029   $267.00   $267.00   $267.00  
  7 purchase totals = $975.49       $1,040.1773   $1,040.18   $1,040.20   $1,040.10