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 $183.66   12.260%   $206.1767   $206.18   $206.20   $206.20  
  Purchase #2 $185.37   4.760%   $194.1936   $194.19   $194.20   $194.20  
  Purchase #3 $132.68   4.444%   $138.5763   $138.58   $138.60   $138.60  
  Purchase #4 $145.57   11.319%   $162.0471   $162.05   $162.05   $162.00  
  Purchase #5 $183.61   3.401%   $189.8546   $189.85   $189.85   $189.90  
  Purchase #6 $54.90   3.709%   $56.9362   $56.94   $56.95   $56.90  
  Purchase #7 $98.34   13.531%   $111.6464   $111.65   $111.65   $111.60  
  7 purchase totals = $984.13       $1,059.4309   $1,059.44   $1,059.50   $1,059.40