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 $73.36   5.714%   $77.5518   $77.55   $77.55   $77.60  
  Purchase #2 $6.90   11.489%   $7.6927   $7.69   $7.70   $7.70  
  Purchase #3 $101.46   5.701%   $107.2442   $107.24   $107.25   $107.20  
  Purchase #4 $241.64   6.785%   $258.0353   $258.04   $258.05   $258.00  
  Purchase #5 $14.52   12.433%   $16.3253   $16.33   $16.35   $16.30  
  Purchase #6 $72.78   5.720%   $76.943   $76.94   $76.95   $76.90  
  Purchase #7 $242.69   3.570%   $251.354   $251.35   $251.35   $251.40  
  7 purchase totals = $753.35       $795.1463   $795.14   $795.20   $795.10