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 $181.61   10.666%   $200.9805   $200.98   $201.00   $201.00  
  Purchase #2 $245.74   8.661%   $267.0235   $267.02   $267.00   $267.00  
  Purchase #3 $93.76   8.518%   $101.7465   $101.75   $101.75   $101.70  
  Purchase #4 $98.45   3.169%   $101.5699   $101.57   $101.55   $101.60  
  Purchase #5 $250.49   3.208%   $258.5257   $258.53   $258.55   $258.50  
  Purchase #6 $13.94   6.342%   $14.8241   $14.82   $14.80   $14.80  
  Purchase #7 $179.78   11.789%   $200.9743   $200.97   $200.95   $201.00  
  7 purchase totals = $1,063.77       $1,145.6445   $1,145.64   $1,145.60   $1,145.60