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 $103.97   6.303%   $110.5232   $110.52   $110.50   $110.50  
  Purchase #2 $178.87   8.423%   $193.9362   $193.94   $193.95   $193.90  
  Purchase #3 $54.56   7.741%   $58.7835   $58.78   $58.80   $58.80  
  Purchase #4 $32.56   5.835%   $34.4599   $34.46   $34.45   $34.50  
  Purchase #5 $113.77   5.591%   $120.1309   $120.13   $120.15   $120.10  
  Purchase #6 $186.64   6.520%   $198.8089   $198.81   $198.80   $198.80  
  Purchase #7 $135.59   7.386%   $145.6047   $145.60   $145.60   $145.60  
  7 purchase totals = $805.96       $862.2473   $862.24   $862.25   $862.20