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 $114.34   5.790%   $120.9603   $120.96   $120.95   $121.00  
  Purchase #2 $201.48   5.116%   $211.7877   $211.79   $211.80   $211.80  
  Purchase #3 $152.90   13.369%   $173.3412   $173.34   $173.35   $173.30  
  Purchase #4 $86.99   12.647%   $97.9916   $97.99   $98.00   $98.00  
  Purchase #5 $113.58   11.368%   $126.4918   $126.49   $126.50   $126.50  
  Purchase #6 $45.36   3.648%   $47.0147   $47.01   $47.00   $47.00  
  Purchase #7 $84.39   5.511%   $89.0407   $89.04   $89.05   $89.00  
  7 purchase totals = $799.04       $866.6280   $866.62   $866.65   $866.60