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 $58.35   12.373%   $65.5696   $65.57   $65.55   $65.60  
  Purchase #2 $145.77   4.378%   $152.1518   $152.15   $152.15   $152.20  
  Purchase #3 $60.41   10.505%   $66.7561   $66.76   $66.75   $66.80  
  Purchase #4 $214.29   5.486%   $226.0459   $226.05   $226.05   $226.00  
  Purchase #5 $45.72   5.426%   $48.2008   $48.20   $48.20   $48.20  
  Purchase #6 $138.46   12.127%   $155.251   $155.25   $155.25   $155.30  
  Purchase #7 $183.33   12.124%   $205.5569   $205.56   $205.55   $205.60  
  7 purchase totals = $846.33       $919.5321   $919.54   $919.50   $919.70