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 $239.27   5.336%   $252.0374   $252.04   $252.05   $252.00  
  Purchase #2 $66.71   8.621%   $72.4611   $72.46   $72.45   $72.50  
  Purchase #3 $180.57   13.750%   $205.3984   $205.40   $205.40   $205.40  
  Purchase #4 $235.65   13.409%   $267.2483   $267.25   $267.25   $267.20  
  Purchase #5 $204.57   4.836%   $214.463   $214.46   $214.45   $214.50  
  Purchase #6 $181.61   11.163%   $201.8831   $201.88   $201.90   $201.90  
  Purchase #7 $187.57   7.219%   $201.1107   $201.11   $201.10   $201.10  
  7 purchase totals = $1,295.95       $1,414.6020   $1,414.60   $1,414.60   $1,414.60