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 $57.82   13.329%   $65.5268   $65.53   $65.55   $65.50  
  Purchase #2 $162.28   8.253%   $175.673   $175.67   $175.65   $175.70  
  Purchase #3 $58.60   7.556%   $63.0278   $63.03   $63.05   $63.00  
  Purchase #4 $246.48   13.336%   $279.3506   $279.35   $279.35   $279.40  
  Purchase #5 $13.81   11.608%   $15.4131   $15.41   $15.40   $15.40  
  Purchase #6 $82.32   4.599%   $86.1059   $86.11   $86.10   $86.10  
  Purchase #7 $226.79   6.219%   $240.8941   $240.89   $240.90   $240.90  
  7 purchase totals = $848.10       $925.9913   $925.99   $926.00   $926.00