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 $242.61   10.171%   $267.2859   $267.29   $267.30   $267.30  
  Purchase #2 $123.72   9.235%   $135.1455   $135.15   $135.15   $135.10  
  Purchase #3 $87.80   11.285%   $97.7082   $97.71   $97.70   $97.70  
  Purchase #4 $194.79   6.238%   $206.941   $206.94   $206.95   $206.90  
  Purchase #5 $109.43   12.130%   $122.7039   $122.70   $122.70   $122.70  
  Purchase #6 $68.25   4.337%   $71.21   $71.21   $71.20   $71.20  
  Purchase #7 $142.72   7.437%   $153.3341   $153.33   $153.35   $153.30  
  7 purchase totals = $969.32       $1,054.3286   $1,054.33   $1,054.35   $1,054.20