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 $61.45   8.704%   $66.7986   $66.80   $66.80   $66.80  
  Purchase #2 $91.84   11.815%   $102.6909   $102.69   $102.70   $102.70  
  Purchase #3 $14.34   11.696%   $16.0172   $16.02   $16.00   $16.00  
  Purchase #4 $5.91   12.134%   $6.6271   $6.63   $6.65   $6.60  
  Purchase #5 $168.76   7.135%   $180.801   $180.80   $180.80   $180.80  
  Purchase #6 $205.90   11.829%   $230.2559   $230.26   $230.25   $230.30  
  Purchase #7 $134.58   12.210%   $151.0122   $151.01   $151.00   $151.00  
  7 purchase totals = $682.78       $754.2029   $754.21   $754.20   $754.20