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 $61.25   4.181%   $63.8109   $63.81   $63.80   $63.80  
  Purchase #2 $239.41   11.719%   $267.4665   $267.47   $267.45   $267.50  
  Purchase #3 $204.38   10.414%   $225.6641   $225.66   $225.65   $225.70  
  Purchase #4 $124.79   10.244%   $137.5735   $137.57   $137.55   $137.60  
  Purchase #5 $197.88   6.164%   $210.0773   $210.08   $210.10   $210.10  
  Purchase #6 $136.84   10.833%   $151.6639   $151.66   $151.65   $151.70  
  Purchase #7 $118.52   6.601%   $126.3435   $126.34   $126.35   $126.30  
  7 purchase totals = $1,083.07       $1,182.5997   $1,182.59   $1,182.55   $1,182.70