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 $48.45   5.725%   $51.2238   $51.22   $51.20   $51.20  
  Purchase #2 $41.99   9.661%   $46.0467   $46.05   $46.05   $46.00  
  Purchase #3 $5.69   5.715%   $6.0152   $6.02   $6.00   $6.00  
  Purchase #4 $5.75   3.231%   $5.9358   $5.94   $5.95   $5.90  
  Purchase #5 $212.74   13.829%   $242.1598   $242.16   $242.15   $242.20  
  Purchase #6 $27.87   5.463%   $29.3925   $29.39   $29.40   $29.40  
  Purchase #7 $100.62   5.630%   $106.2849   $106.28   $106.30   $106.30  
  7 purchase totals = $443.11       $487.0587   $487.06   $487.05   $487.00