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 $106.46   5.839%   $112.6762   $112.68   $112.70   $112.70  
  Purchase #2 $155.72   11.695%   $173.9315   $173.93   $173.95   $173.90  
  Purchase #3 $248.70   6.309%   $264.3905   $264.39   $264.40   $264.40  
  Purchase #4 $43.77   13.434%   $49.6501   $49.65   $49.65   $49.70  
  Purchase #5 $138.78   8.658%   $150.7956   $150.80   $150.80   $150.80  
  Purchase #6 $249.78   8.607%   $271.2786   $271.28   $271.30   $271.30  
  Purchase #7 $127.32   12.688%   $143.4744   $143.47   $143.45   $143.50  
  7 purchase totals = $1,070.53       $1,166.1969   $1,166.20   $1,166.25   $1,166.30