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 $32.97   13.133%   $37.3   $37.30   $37.30   $37.30  
  Purchase #2 $227.60   3.249%   $234.9947   $234.99   $235.00   $235.00  
  Purchase #3 $198.73   13.812%   $226.1786   $226.18   $226.20   $226.20  
  Purchase #4 $246.32   3.349%   $254.5693   $254.57   $254.55   $254.60  
  Purchase #5 $66.51   3.183%   $68.627   $68.63   $68.65   $68.60  
  Purchase #6 $250.82   6.301%   $266.6242   $266.62   $266.60   $266.60  
  Purchase #7 $167.54   5.571%   $176.8737   $176.87   $176.85   $176.90  
  7 purchase totals = $1,190.49       $1,265.1675   $1,265.16   $1,265.15   $1,265.20