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 $165.76   9.464%   $181.4475   $181.45   $181.45   $181.40  
  Purchase #2 $64.99   13.271%   $73.6148   $73.61   $73.60   $73.60  
  Purchase #3 $147.90   5.414%   $155.9073   $155.91   $155.90   $155.90  
  Purchase #4 $131.39   6.247%   $139.5979   $139.60   $139.60   $139.60  
  Purchase #5 $200.34   6.126%   $212.6128   $212.61   $212.60   $212.60  
  Purchase #6 $169.81   4.682%   $177.7605   $177.76   $177.75   $177.80  
  Purchase #7 $161.80   7.755%   $174.3476   $174.35   $174.35   $174.30  
  7 purchase totals = $1,041.99       $1,115.2884   $1,115.29   $1,115.25   $1,115.20