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 $42.52   9.589%   $46.5972   $46.60   $46.60   $46.60  
  Purchase #2 $119.58   13.521%   $135.7484   $135.75   $135.75   $135.70  
  Purchase #3 $176.64   4.355%   $184.3327   $184.33   $184.35   $184.30  
  Purchase #4 $195.35   3.677%   $202.533   $202.53   $202.55   $202.50  
  Purchase #5 $11.76   9.175%   $12.839   $12.84   $12.85   $12.80  
  Purchase #6 $182.28   10.843%   $202.0446   $202.04   $202.05   $202.00  
  Purchase #7 $218.95   9.498%   $239.7459   $239.75   $239.75   $239.70  
  7 purchase totals = $947.08       $1,023.8408   $1,023.84   $1,023.90   $1,023.60