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 $176.68   13.113%   $199.848   $199.85   $199.85   $199.80  
  Purchase #2 $46.90   3.291%   $48.4435   $48.44   $48.45   $48.40  
  Purchase #3 $108.91   8.433%   $118.0944   $118.09   $118.10   $118.10  
  Purchase #4 $89.64   7.790%   $96.623   $96.62   $96.60   $96.60  
  Purchase #5 $215.27   11.727%   $240.5147   $240.51   $240.50   $240.50  
  Purchase #6 $166.44   8.862%   $181.1899   $181.19   $181.20   $181.20  
  Purchase #7 $186.72   4.410%   $194.9544   $194.95   $194.95   $195.00  
  7 purchase totals = $990.56       $1,079.6679   $1,079.65   $1,079.65   $1,079.60