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 $192.43   5.838%   $203.6641   $203.66   $203.65   $203.70  
  Purchase #2 $27.34   7.505%   $29.3919   $29.39   $29.40   $29.40  
  Purchase #3 $105.50   3.442%   $109.1313   $109.13   $109.15   $109.10  
  Purchase #4 $96.63   7.151%   $103.54   $103.54   $103.55   $103.50  
  Purchase #5 $244.91   9.526%   $268.2401   $268.24   $268.25   $268.20  
  Purchase #6 $106.56   6.510%   $113.4971   $113.50   $113.50   $113.50  
  Purchase #7 $209.96   12.112%   $235.3904   $235.39   $235.40   $235.40  
  7 purchase totals = $983.33       $1,062.8549   $1,062.85   $1,062.90   $1,062.80