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 $167.47   10.478%   $185.0175   $185.02   $185.00   $185.00  
  Purchase #2 $91.38   4.866%   $95.8266   $95.83   $95.85   $95.80  
  Purchase #3 $31.58   10.704%   $34.9603   $34.96   $34.95   $35.00  
  Purchase #4 $225.74   13.421%   $256.0366   $256.04   $256.05   $256.00  
  Purchase #5 $75.45   8.805%   $82.0934   $82.09   $82.10   $82.10  
  Purchase #6 $126.60   3.395%   $130.8981   $130.90   $130.90   $130.90  
  Purchase #7 $249.69   7.829%   $269.2382   $269.24   $269.25   $269.20  
  7 purchase totals = $967.91       $1,054.0707   $1,054.08   $1,054.10   $1,054.00