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 $237.91   12.359%   $267.3133   $267.31   $267.30   $267.30  
  Purchase #2 $112.64   6.173%   $119.5933   $119.59   $119.60   $119.60  
  Purchase #3 $22.90   13.676%   $26.0318   $26.03   $26.05   $26.00  
  Purchase #4 $84.46   7.583%   $90.8646   $90.86   $90.85   $90.90  
  Purchase #5 $112.46   5.651%   $118.8151   $118.82   $118.80   $118.80  
  Purchase #6 $36.51   12.384%   $41.0314   $41.03   $41.05   $41.00  
  Purchase #7 $189.78   11.174%   $210.986   $210.99   $211.00   $211.00  
  7 purchase totals = $796.66       $874.6355   $874.63   $874.65   $874.60