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 $58.57   6.104%   $62.1451   $62.15   $62.15   $62.10  
  Purchase #2 $151.69   11.678%   $169.4044   $169.40   $169.40   $169.40  
  Purchase #3 $16.84   9.669%   $18.4683   $18.47   $18.45   $18.50  
  Purchase #4 $157.84   7.811%   $170.1689   $170.17   $170.15   $170.20  
  Purchase #5 $144.85   12.809%   $163.4038   $163.40   $163.40   $163.40  
  Purchase #6 $146.54   5.651%   $154.821   $154.82   $154.80   $154.80  
  Purchase #7 $5.61   3.564%   $5.8099   $5.81   $5.80   $5.80  
  7 purchase totals = $681.94       $744.2214   $744.22   $744.15   $744.20