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 $194.29   12.726%   $219.0153   $219.02   $219.00   $219.00  
  Purchase #2 $169.90   4.235%   $177.0953   $177.10   $177.10   $177.10  
  Purchase #3 $32.85   10.369%   $36.2562   $36.26   $36.25   $36.30  
  Purchase #4 $134.35   7.859%   $144.9086   $144.91   $144.90   $144.90  
  Purchase #5 $109.87   8.158%   $118.8332   $118.83   $118.85   $118.80  
  Purchase #6 $239.41   11.626%   $267.2438   $267.24   $267.25   $267.20  
  Purchase #7 $77.81   13.838%   $88.5773   $88.58   $88.60   $88.60  
  7 purchase totals = $958.48       $1,051.9297   $1,051.94   $1,051.95   $1,051.90