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 $192.41   11.613%   $214.7546   $214.75   $214.75   $214.80  
  Purchase #2 $176.53   10.865%   $195.71   $195.71   $195.70   $195.70  
  Purchase #3 $169.54   11.524%   $189.0778   $189.08   $189.10   $189.10  
  Purchase #4 $106.32   9.470%   $116.3885   $116.39   $116.40   $116.40  
  Purchase #5 $110.76   10.494%   $122.3832   $122.38   $122.40   $122.40  
  Purchase #6 $29.89   10.363%   $32.9875   $32.99   $33.00   $33.00  
  Purchase #7 $77.25   3.556%   $79.997   $80.00   $80.00   $80.00  
  7 purchase totals = $862.70       $951.2986   $951.30   $951.35   $951.40