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 $241.97   3.546%   $250.5503   $250.55   $250.55   $250.60  
  Purchase #2 $176.77   8.861%   $192.4336   $192.43   $192.45   $192.40  
  Purchase #3 $226.72   3.509%   $234.6756   $234.68   $234.70   $234.70  
  Purchase #4 $67.51   10.359%   $74.5034   $74.50   $74.50   $74.50  
  Purchase #5 $43.82   3.783%   $45.4777   $45.48   $45.50   $45.50  
  Purchase #6 $226.50   9.475%   $247.9609   $247.96   $247.95   $248.00  
  Purchase #7 $72.42   3.865%   $75.219   $75.22   $75.20   $75.20  
  7 purchase totals = $1,055.71       $1,120.8205   $1,120.82   $1,120.85   $1,120.90