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 $100.40   7.489%   $107.919   $107.92   $107.90   $107.90  
  Purchase #2 $67.88   11.349%   $75.5837   $75.58   $75.60   $75.60  
  Purchase #3 $71.51   5.729%   $75.6068   $75.61   $75.60   $75.60  
  Purchase #4 $159.36   4.579%   $166.6571   $166.66   $166.65   $166.70  
  Purchase #5 $77.53   10.368%   $85.5683   $85.57   $85.55   $85.60  
  Purchase #6 $107.61   11.356%   $119.8302   $119.83   $119.85   $119.80  
  Purchase #7 $16.60   3.411%   $17.1662   $17.17   $17.15   $17.20  
  7 purchase totals = $600.89       $648.3313   $648.34   $648.30   $648.40