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 $140.58   5.662%   $148.5396   $148.54   $148.55   $148.50  
  Purchase #2 $168.83   5.311%   $177.7966   $177.80   $177.80   $177.80  
  Purchase #3 $55.37   9.665%   $60.7215   $60.72   $60.70   $60.70  
  Purchase #4 $165.40   4.112%   $172.2012   $172.20   $172.20   $172.20  
  Purchase #5 $142.33   9.185%   $155.403   $155.40   $155.40   $155.40  
  Purchase #6 $172.72   7.654%   $185.94   $185.94   $185.95   $185.90  
  Purchase #7 $127.43   8.455%   $138.2042   $138.20   $138.20   $138.20  
  7 purchase totals = $972.66       $1,038.8061   $1,038.80   $1,038.80   $1,038.70