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 $126.90   8.861%   $138.1446   $138.14   $138.15   $138.10  
  Purchase #2 $241.39   4.614%   $252.5277   $252.53   $252.55   $252.50  
  Purchase #3 $215.92   13.231%   $244.4884   $244.49   $244.50   $244.50  
  Purchase #4 $70.95   9.767%   $77.8797   $77.88   $77.90   $77.90  
  Purchase #5 $6.42   3.429%   $6.6401   $6.64   $6.65   $6.60  
  Purchase #6 $102.44   4.318%   $106.8634   $106.86   $106.85   $106.90  
  Purchase #7 $64.97   5.530%   $68.5628   $68.56   $68.55   $68.60  
  7 purchase totals = $828.99       $895.1067   $895.10   $895.15   $895.10