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 $65.97   4.812%   $69.1445   $69.14   $69.15   $69.10  
  Purchase #2 $61.27   4.294%   $63.9009   $63.90   $63.90   $63.90  
  Purchase #3 $27.91   5.811%   $29.5319   $29.53   $29.55   $29.50  
  Purchase #4 $183.62   4.862%   $192.5476   $192.55   $192.55   $192.50  
  Purchase #5 $140.44   4.320%   $146.507   $146.51   $146.50   $146.50  
  Purchase #6 $197.28   11.548%   $220.0619   $220.06   $220.05   $220.10  
  Purchase #7 $158.62   10.180%   $174.7675   $174.77   $174.75   $174.80  
  7 purchase totals = $835.11       $896.4613   $896.46   $896.45   $896.40