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 $106.77   11.849%   $119.4212   $119.42   $119.40   $119.40  
  Purchase #2 $191.74   5.841%   $202.9395   $202.94   $202.95   $202.90  
  Purchase #3 $145.43   13.440%   $164.9758   $164.98   $165.00   $165.00  
  Purchase #4 $45.61   7.583%   $49.0686   $49.07   $49.05   $49.10  
  Purchase #5 $224.67   11.665%   $250.8778   $250.88   $250.90   $250.90  
  Purchase #6 $7.72   7.818%   $8.3235   $8.32   $8.30   $8.30  
  Purchase #7 $68.30   4.871%   $71.6269   $71.63   $71.65   $71.60  
  7 purchase totals = $790.24       $867.2333   $867.24   $867.25   $867.20