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 $93.64   9.379%   $102.4225   $102.42   $102.40   $102.40  
  Purchase #2 $142.82   6.405%   $151.9676   $151.97   $151.95   $152.00  
  Purchase #3 $22.25   8.472%   $24.135   $24.14   $24.15   $24.10  
  Purchase #4 $197.51   5.783%   $208.932   $208.93   $208.95   $208.90  
  Purchase #5 $53.78   5.571%   $56.7761   $56.78   $56.80   $56.80  
  Purchase #6 $206.51   9.238%   $225.5874   $225.59   $225.60   $225.60  
  Purchase #7 $160.70   13.251%   $181.9944   $181.99   $182.00   $182.00  
  7 purchase totals = $877.21       $951.8150   $951.82   $951.85   $951.80