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 $154.67   5.815%   $163.6641   $163.66   $163.65   $163.70  
  Purchase #2 $128.45   4.266%   $133.9297   $133.93   $133.95   $133.90  
  Purchase #3 $26.58   11.707%   $29.6917   $29.69   $29.70   $29.70  
  Purchase #4 $173.40   10.199%   $191.0851   $191.09   $191.10   $191.10  
  Purchase #5 $114.98   3.137%   $118.5869   $118.59   $118.60   $118.60  
  Purchase #6 $9.96   13.332%   $11.2879   $11.29   $11.30   $11.30  
  Purchase #7 $118.32   5.497%   $124.8241   $124.82   $124.80   $124.80  
  7 purchase totals = $726.36       $773.0695   $773.07   $773.10   $773.10