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 $86.51   12.159%   $97.0288   $97.03   $97.05   $97.00  
  Purchase #2 $150.99   12.116%   $169.2839   $169.28   $169.30   $169.30  
  Purchase #3 $116.55   4.115%   $121.346   $121.35   $121.35   $121.30  
  Purchase #4 $176.30   4.381%   $184.0237   $184.02   $184.00   $184.00  
  Purchase #5 $166.75   9.540%   $182.658   $182.66   $182.65   $182.70  
  Purchase #6 $79.76   13.514%   $90.5388   $90.54   $90.55   $90.50  
  Purchase #7 $135.37   8.861%   $147.3651   $147.37   $147.35   $147.40  
  7 purchase totals = $912.23       $992.2443   $992.25   $992.25   $992.20