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 $137.64   5.638%   $145.4001   $145.40   $145.40   $145.40  
  Purchase #2 $18.46   10.248%   $20.3518   $20.35   $20.35   $20.40  
  Purchase #3 $100.57   6.231%   $106.8365   $106.84   $106.85   $106.80  
  Purchase #4 $162.94   13.153%   $184.3715   $184.37   $184.35   $184.40  
  Purchase #5 $143.63   13.800%   $163.4509   $163.45   $163.45   $163.50  
  Purchase #6 $32.53   5.868%   $34.4389   $34.44   $34.45   $34.40  
  Purchase #7 $59.58   6.334%   $63.3538   $63.35   $63.35   $63.40  
  7 purchase totals = $655.35       $718.2035   $718.20   $718.20   $718.30