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 $52.26   13.253%   $59.186   $59.19   $59.20   $59.20  
  Purchase #2 $42.67   10.706%   $47.2383   $47.24   $47.25   $47.20  
  Purchase #3 $102.69   8.580%   $111.5008   $111.50   $111.50   $111.50  
  Purchase #4 $246.93   8.869%   $268.8302   $268.83   $268.85   $268.80  
  Purchase #5 $194.95   12.376%   $219.077   $219.08   $219.10   $219.10  
  Purchase #6 $67.67   7.346%   $72.641   $72.64   $72.65   $72.60  
  Purchase #7 $10.47   11.460%   $11.6699   $11.67   $11.65   $11.70  
  7 purchase totals = $717.64       $790.1432   $790.15   $790.20   $790.10