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 $124.97   9.274%   $136.5597   $136.56   $136.55   $136.60  
  Purchase #2 $145.40   8.463%   $157.7052   $157.71   $157.70   $157.70  
  Purchase #3 $83.42   12.701%   $94.0152   $94.02   $94.00   $94.00  
  Purchase #4 $236.89   12.558%   $266.6386   $266.64   $266.65   $266.60  
  Purchase #5 $67.43   11.545%   $75.2148   $75.21   $75.20   $75.20  
  Purchase #6 $247.88   6.304%   $263.5064   $263.51   $263.50   $263.50  
  Purchase #7 $192.99   12.128%   $216.3958   $216.40   $216.40   $216.40  
  7 purchase totals = $1,098.98       $1,210.0357   $1,210.05   $1,210.00   $1,210.00