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 $137.75   7.737%   $148.4077   $148.41   $148.40   $148.40  
  Purchase #2 $108.78   7.162%   $116.5708   $116.57   $116.55   $116.60  
  Purchase #3 $105.32   5.251%   $110.8504   $110.85   $110.85   $110.90  
  Purchase #4 $237.76   8.638%   $258.2977   $258.30   $258.30   $258.30  
  Purchase #5 $99.49   8.830%   $108.275   $108.28   $108.30   $108.30  
  Purchase #6 $174.33   7.366%   $187.1711   $187.17   $187.15   $187.20  
  Purchase #7 $249.62   3.503%   $258.3642   $258.36   $258.35   $258.40  
  7 purchase totals = $1,113.05       $1,187.9369   $1,187.94   $1,187.90   $1,188.10