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 $149.57   8.530%   $162.3283   $162.33   $162.35   $162.30  
  Purchase #2 $153.90   7.440%   $165.3502   $165.35   $165.35   $165.40  
  Purchase #3 $49.39   12.313%   $55.4714   $55.47   $55.45   $55.50  
  Purchase #4 $101.32   10.211%   $111.6658   $111.67   $111.65   $111.70  
  Purchase #5 $236.30   11.658%   $263.8479   $263.85   $263.85   $263.80  
  Purchase #6 $205.25   4.503%   $214.4924   $214.49   $214.50   $214.50  
  Purchase #7 $25.67   3.538%   $26.5782   $26.58   $26.60   $26.60  
  7 purchase totals = $921.40       $999.7342   $999.74   $999.75   $999.80