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 $224.83   11.570%   $250.8428   $250.84   $250.85   $250.80  
  Purchase #2 $73.91   3.818%   $76.7319   $76.73   $76.75   $76.70  
  Purchase #3 $122.83   6.461%   $130.766   $130.77   $130.75   $130.80  
  Purchase #4 $247.99   6.776%   $264.7938   $264.79   $264.80   $264.80  
  Purchase #5 $86.77   6.102%   $92.0647   $92.06   $92.05   $92.10  
  Purchase #6 $151.47   11.844%   $169.4101   $169.41   $169.40   $169.40  
  Purchase #7 $25.95   4.364%   $27.0825   $27.08   $27.10   $27.10  
  7 purchase totals = $933.75       $1,011.6918   $1,011.68   $1,011.70   $1,011.70