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 $62.87   6.364%   $66.871   $66.87   $66.85   $66.90  
  Purchase #2 $230.82   6.764%   $246.4327   $246.43   $246.45   $246.40  
  Purchase #3 $64.64   9.147%   $70.5526   $70.55   $70.55   $70.60  
  Purchase #4 $237.95   4.727%   $249.1979   $249.20   $249.20   $249.20  
  Purchase #5 $190.73   5.874%   $201.9335   $201.93   $201.95   $201.90  
  Purchase #6 $37.64   8.660%   $40.8996   $40.90   $40.90   $40.90  
  Purchase #7 $129.67   3.159%   $133.7663   $133.77   $133.75   $133.80  
  7 purchase totals = $954.32       $1,009.6536   $1,009.65   $1,009.65   $1,009.70