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 $152.64   8.743%   $165.9853   $165.99   $166.00   $166.00  
  Purchase #2 $250.61   7.658%   $269.8017   $269.80   $269.80   $269.80  
  Purchase #3 $95.42   9.766%   $104.7387   $104.74   $104.75   $104.70  
  Purchase #4 $39.65   9.554%   $43.4382   $43.44   $43.45   $43.40  
  Purchase #5 $239.66   11.110%   $266.2862   $266.29   $266.30   $266.30  
  Purchase #6 $248.50   6.708%   $265.1694   $265.17   $265.15   $265.20  
  Purchase #7 $135.58   12.489%   $152.5126   $152.51   $152.50   $152.50  
  7 purchase totals = $1,162.06       $1,267.9321   $1,267.94   $1,267.95   $1,267.90