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 $179.92   10.376%   $198.5885   $198.59   $198.60   $198.60  
  Purchase #2 $129.33   11.274%   $143.9107   $143.91   $143.90   $143.90  
  Purchase #3 $223.93   9.424%   $245.0332   $245.03   $245.05   $245.00  
  Purchase #4 $60.56   11.533%   $67.5444   $67.54   $67.55   $67.50  
  Purchase #5 $22.51   3.671%   $23.3363   $23.34   $23.35   $23.30  
  Purchase #6 $240.49   5.564%   $253.8709   $253.87   $253.85   $253.90  
  Purchase #7 $86.25   5.559%   $91.0446   $91.04   $91.05   $91.00  
  7 purchase totals = $942.99       $1,023.3286   $1,023.32   $1,023.35   $1,023.20