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 $123.46   3.369%   $127.6194   $127.62   $127.60   $127.60  
  Purchase #2 $168.44   13.406%   $191.0211   $191.02   $191.00   $191.00  
  Purchase #3 $137.71   10.222%   $151.7867   $151.79   $151.80   $151.80  
  Purchase #4 $24.49   7.306%   $26.2792   $26.28   $26.30   $26.30  
  Purchase #5 $245.34   4.621%   $256.6772   $256.68   $256.70   $256.70  
  Purchase #6 $212.62   5.777%   $224.9031   $224.90   $224.90   $224.90  
  Purchase #7 $114.80   7.156%   $123.0151   $123.02   $123.00   $123.00  
  7 purchase totals = $1,026.86       $1,101.3018   $1,101.31   $1,101.30   $1,101.30