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 $238.61   11.406%   $265.8259   $265.83   $265.85   $265.80  
  Purchase #2 $176.34   12.703%   $198.7405   $198.74   $198.75   $198.70  
  Purchase #3 $158.87   9.476%   $173.9245   $173.92   $173.90   $173.90  
  Purchase #4 $145.65   10.442%   $160.8588   $160.86   $160.85   $160.90  
  Purchase #5 $24.41   10.672%   $27.015   $27.02   $27.00   $27.00  
  Purchase #6 $70.61   7.631%   $75.9982   $76.00   $76.00   $76.00  
  Purchase #7 $106.46   12.828%   $120.1167   $120.12   $120.10   $120.10  
  7 purchase totals = $920.95       $1,022.4796   $1,022.49   $1,022.45   $1,022.40