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 $55.45   8.822%   $60.3418   $60.34   $60.35   $60.30  
  Purchase #2 $179.53   9.615%   $196.7918   $196.79   $196.80   $196.80  
  Purchase #3 $201.73   8.133%   $218.1367   $218.14   $218.15   $218.10  
  Purchase #4 $119.41   8.236%   $129.2446   $129.24   $129.25   $129.20  
  Purchase #5 $13.57   7.641%   $14.6069   $14.61   $14.60   $14.60  
  Purchase #6 $107.46   12.840%   $121.2579   $121.26   $121.25   $121.30  
  Purchase #7 $81.32   7.667%   $87.5548   $87.55   $87.55   $87.60  
  7 purchase totals = $758.47       $827.9345   $827.93   $827.95   $827.90