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 $60.78   7.569%   $65.3804   $65.38   $65.40   $65.40  
  Purchase #2 $127.61   6.321%   $135.6762   $135.68   $135.70   $135.70  
  Purchase #3 $47.65   11.809%   $53.277   $53.28   $53.30   $53.30  
  Purchase #4 $240.93   11.212%   $267.9431   $267.94   $267.95   $267.90  
  Purchase #5 $135.89   8.559%   $147.5208   $147.52   $147.50   $147.50  
  Purchase #6 $199.66   10.804%   $221.2313   $221.23   $221.25   $221.20  
  Purchase #7 $172.32   6.199%   $183.0021   $183.00   $183.00   $183.00  
  7 purchase totals = $984.84       $1,074.0309   $1,074.03   $1,074.10   $1,074.00