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 $96.42   6.120%   $102.3209   $102.32   $102.30   $102.30  
  Purchase #2 $237.39   12.554%   $267.1919   $267.19   $267.20   $267.20  
  Purchase #3 $48.38   9.737%   $53.0908   $53.09   $53.10   $53.10  
  Purchase #4 $112.67   8.699%   $122.4712   $122.47   $122.45   $122.50  
  Purchase #5 $161.96   6.247%   $172.0776   $172.08   $172.10   $172.10  
  Purchase #6 $230.91   3.367%   $238.6847   $238.68   $238.70   $238.70  
  Purchase #7 $99.58   12.324%   $111.8522   $111.85   $111.85   $111.90  
  7 purchase totals = $987.31       $1,067.6893   $1,067.68   $1,067.70   $1,067.80