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 $44.67   8.590%   $48.5072   $48.51   $48.50   $48.50  
  Purchase #2 $112.61   9.737%   $123.5748   $123.57   $123.55   $123.60  
  Purchase #3 $248.28   8.781%   $270.0815   $270.08   $270.10   $270.10  
  Purchase #4 $120.30   5.221%   $126.5809   $126.58   $126.60   $126.60  
  Purchase #5 $32.79   10.788%   $36.3274   $36.33   $36.35   $36.30  
  Purchase #6 $171.56   9.547%   $187.9388   $187.94   $187.95   $187.90  
  Purchase #7 $247.63   10.636%   $273.9679   $273.97   $273.95   $274.00  
  7 purchase totals = $977.84       $1,066.9785   $1,066.98   $1,067.00   $1,067.00