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 $58.69   6.680%   $62.6105   $62.61   $62.60   $62.60  
  Purchase #2 $171.64   5.850%   $181.6809   $181.68   $181.70   $181.70  
  Purchase #3 $187.88   8.636%   $204.1053   $204.11   $204.10   $204.10  
  Purchase #4 $14.58   5.481%   $15.3791   $15.38   $15.40   $15.40  
  Purchase #5 $48.70   8.673%   $52.9238   $52.92   $52.90   $52.90  
  Purchase #6 $237.79   6.125%   $252.3546   $252.35   $252.35   $252.40  
  Purchase #7 $78.65   9.109%   $85.8142   $85.81   $85.80   $85.80  
  7 purchase totals = $797.93       $854.8684   $854.86   $854.85   $854.90