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 $47.94   8.162%   $51.8529   $51.85   $51.85   $51.90  
  Purchase #2 $124.67   10.294%   $137.5035   $137.50   $137.50   $137.50  
  Purchase #3 $161.95   9.441%   $177.2397   $177.24   $177.25   $177.20  
  Purchase #4 $107.51   11.682%   $120.0693   $120.07   $120.05   $120.10  
  Purchase #5 $231.42   8.404%   $250.8685   $250.87   $250.85   $250.90  
  Purchase #6 $97.31   8.186%   $105.2758   $105.28   $105.30   $105.30  
  Purchase #7 $197.28   7.783%   $212.6343   $212.63   $212.65   $212.60  
  7 purchase totals = $968.08       $1,055.4440   $1,055.44   $1,055.45   $1,055.50