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 $234.57   7.556%   $252.2941   $252.29   $252.30   $252.30  
  Purchase #2 $68.69   10.656%   $76.0096   $76.01   $76.00   $76.00  
  Purchase #3 $155.72   13.419%   $176.6161   $176.62   $176.60   $176.60  
  Purchase #4 $149.36   10.311%   $164.7605   $164.76   $164.75   $164.80  
  Purchase #5 $219.57   13.350%   $248.8826   $248.88   $248.90   $248.90  
  Purchase #6 $56.42   7.799%   $60.8202   $60.82   $60.80   $60.80  
  Purchase #7 $37.84   4.592%   $39.5776   $39.58   $39.60   $39.60  
  7 purchase totals = $922.17       $1,018.9607   $1,018.96   $1,018.95   $1,019.00