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 $61.91   11.612%   $69.099   $69.10   $69.10   $69.10  
  Purchase #2 $56.27   8.446%   $61.0226   $61.02   $61.00   $61.00  
  Purchase #3 $94.92   12.454%   $106.7413   $106.74   $106.75   $106.70  
  Purchase #4 $67.59   11.411%   $75.3027   $75.30   $75.30   $75.30  
  Purchase #5 $203.45   5.673%   $214.9917   $214.99   $215.00   $215.00  
  Purchase #6 $106.30   5.306%   $111.9403   $111.94   $111.95   $111.90  
  Purchase #7 $10.72   7.556%   $11.53   $11.53   $11.55   $11.50  
  7 purchase totals = $601.16       $650.6276   $650.62   $650.65   $650.50