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 $130.41   3.126%   $134.4866   $134.49   $134.50   $134.50  
  Purchase #2 $190.50   12.727%   $214.7449   $214.74   $214.75   $214.70  
  Purchase #3 $152.98   13.224%   $173.2101   $173.21   $173.20   $173.20  
  Purchase #4 $75.68   11.275%   $84.2129   $84.21   $84.20   $84.20  
  Purchase #5 $120.91   5.248%   $127.2554   $127.26   $127.25   $127.30  
  Purchase #6 $88.64   7.235%   $95.0531   $95.05   $95.05   $95.10  
  Purchase #7 $219.51   5.333%   $231.2165   $231.22   $231.20   $231.20  
  7 purchase totals = $978.63       $1,060.1795   $1,060.18   $1,060.15   $1,060.20