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 $168.28   6.386%   $179.0264   $179.03   $179.05   $179.00  
  Purchase #2 $190.54   6.680%   $203.2681   $203.27   $203.25   $203.30  
  Purchase #3 $187.72   3.803%   $194.859   $194.86   $194.85   $194.90  
  Purchase #4 $75.86   5.344%   $79.914   $79.91   $79.90   $79.90  
  Purchase #5 $67.45   8.695%   $73.3148   $73.31   $73.30   $73.30  
  Purchase #6 $240.43   12.349%   $270.1207   $270.12   $270.10   $270.10  
  Purchase #7 $21.85   4.868%   $22.9137   $22.91   $22.90   $22.90  
  7 purchase totals = $952.13       $1,023.4167   $1,023.41   $1,023.35   $1,023.40