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 $55.92   12.808%   $63.0822   $63.08   $63.10   $63.10  
  Purchase #2 $241.84   11.157%   $268.8221   $268.82   $268.80   $268.80  
  Purchase #3 $165.89   4.683%   $173.6586   $173.66   $173.65   $173.70  
  Purchase #4 $145.76   12.618%   $164.152   $164.15   $164.15   $164.20  
  Purchase #5 $208.51   6.260%   $221.5627   $221.56   $221.55   $221.60  
  Purchase #6 $145.44   13.458%   $165.0133   $165.01   $165.00   $165.00  
  Purchase #7 $20.66   9.532%   $22.6293   $22.63   $22.65   $22.60  
  7 purchase totals = $984.02       $1,078.9202   $1,078.91   $1,078.90   $1,079.00