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 $63.98   5.824%   $67.7062   $67.71   $67.70   $67.70  
  Purchase #2 $58.72   3.281%   $60.6466   $60.65   $60.65   $60.60  
  Purchase #3 $217.58   3.684%   $225.5956   $225.60   $225.60   $225.60  
  Purchase #4 $118.87   4.786%   $124.5591   $124.56   $124.55   $124.60  
  Purchase #5 $8.41   7.819%   $9.0676   $9.07   $9.05   $9.10  
  Purchase #6 $221.46   3.628%   $229.4946   $229.49   $229.50   $229.50  
  Purchase #7 $163.39   12.147%   $183.237   $183.24   $183.25   $183.20  
  7 purchase totals = $852.41       $900.3067   $900.32   $900.30   $900.30