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 $214.54   8.172%   $232.0722   $232.07   $232.05   $232.10  
  Purchase #2 $114.98   11.293%   $127.9647   $127.96   $127.95   $128.00  
  Purchase #3 $156.77   6.133%   $166.3847   $166.38   $166.40   $166.40  
  Purchase #4 $187.96   13.108%   $212.5978   $212.60   $212.60   $212.60  
  Purchase #5 $92.45   5.754%   $97.7696   $97.77   $97.75   $97.80  
  Purchase #6 $155.97   11.768%   $174.3245   $174.32   $174.30   $174.30  
  Purchase #7 $227.60   6.209%   $241.7317   $241.73   $241.75   $241.70  
  7 purchase totals = $1,150.27       $1,252.8452   $1,252.83   $1,252.80   $1,252.90