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 $233.83   13.402%   $265.1679   $265.17   $265.15   $265.20  
  Purchase #2 $146.49   5.134%   $154.0108   $154.01   $154.00   $154.00  
  Purchase #3 $97.72   9.819%   $107.3151   $107.32   $107.30   $107.30  
  Purchase #4 $34.87   3.279%   $36.0134   $36.01   $36.00   $36.00  
  Purchase #5 $24.83   6.124%   $26.3506   $26.35   $26.35   $26.40  
  Purchase #6 $40.71   11.490%   $45.3876   $45.39   $45.40   $45.40  
  Purchase #7 $212.83   9.303%   $232.6296   $232.63   $232.65   $232.60  
  7 purchase totals = $791.28       $866.8750   $866.88   $866.85   $866.90