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 $106.48   10.852%   $118.0352   $118.04   $118.05   $118.00  
  Purchase #2 $96.34   13.434%   $109.2823   $109.28   $109.30   $109.30  
  Purchase #3 $77.57   8.765%   $84.369   $84.37   $84.35   $84.40  
  Purchase #4 $97.87   9.623%   $107.288   $107.29   $107.30   $107.30  
  Purchase #5 $52.57   5.233%   $55.321   $55.32   $55.30   $55.30  
  Purchase #6 $221.91   10.225%   $244.6003   $244.60   $244.60   $244.60  
  Purchase #7 $179.49   9.625%   $196.7659   $196.77   $196.75   $196.80  
  7 purchase totals = $832.23       $915.6617   $915.67   $915.65   $915.70