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 $77.45   11.485%   $86.3451   $86.35   $86.35   $86.30  
  Purchase #2 $144.40   3.620%   $149.6273   $149.63   $149.65   $149.60  
  Purchase #3 $149.41   8.765%   $162.5058   $162.51   $162.50   $162.50  
  Purchase #4 $241.87   3.428%   $250.1613   $250.16   $250.15   $250.20  
  Purchase #5 $32.99   5.449%   $34.7876   $34.79   $34.80   $34.80  
  Purchase #6 $219.32   12.313%   $246.3249   $246.32   $246.30   $246.30  
  Purchase #7 $116.73   4.603%   $122.1031   $122.10   $122.10   $122.10  
  7 purchase totals = $982.17       $1,051.8551   $1,051.86   $1,051.85   $1,051.80