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 $46.58   6.701%   $49.7013   $49.70   $49.70   $49.70  
  Purchase #2 $81.88   9.388%   $89.5669   $89.57   $89.55   $89.60  
  Purchase #3 $192.59   5.767%   $203.6967   $203.70   $203.70   $203.70  
  Purchase #4 $153.86   12.852%   $173.6341   $173.63   $173.65   $173.60  
  Purchase #5 $171.40   12.310%   $192.4993   $192.50   $192.50   $192.50  
  Purchase #6 $141.35   9.382%   $154.6115   $154.61   $154.60   $154.60  
  Purchase #7 $187.29   7.393%   $201.1363   $201.14   $201.15   $201.10  
  7 purchase totals = $974.95       $1,064.8461   $1,064.85   $1,064.85   $1,064.80