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 $183.73   13.118%   $207.8317   $207.83   $207.85   $207.80  
  Purchase #2 $144.62   8.278%   $156.5916   $156.59   $156.60   $156.60  
  Purchase #3 $130.35   12.309%   $146.3948   $146.39   $146.40   $146.40  
  Purchase #4 $72.48   7.504%   $77.9189   $77.92   $77.90   $77.90  
  Purchase #5 $53.93   11.811%   $60.2997   $60.30   $60.30   $60.30  
  Purchase #6 $193.29   3.267%   $199.6048   $199.60   $199.60   $199.60  
  Purchase #7 $182.39   7.626%   $196.2991   $196.30   $196.30   $196.30  
  7 purchase totals = $960.79       $1,044.9406   $1,044.93   $1,044.95   $1,044.90