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 $218.95   10.392%   $241.7033   $241.70   $241.70   $241.70  
  Purchase #2 $45.92   7.406%   $49.3208   $49.32   $49.30   $49.30  
  Purchase #3 $11.68   13.177%   $13.2191   $13.22   $13.20   $13.20  
  Purchase #4 $202.59   10.104%   $223.0597   $223.06   $223.05   $223.10  
  Purchase #5 $177.64   7.383%   $190.7552   $190.76   $190.75   $190.80  
  Purchase #6 $139.33   4.150%   $145.1122   $145.11   $145.10   $145.10  
  Purchase #7 $162.85   11.252%   $181.1739   $181.17   $181.15   $181.20  
  7 purchase totals = $958.96       $1,044.3442   $1,044.34   $1,044.25   $1,044.40