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 $169.47   13.839%   $192.923   $192.92   $192.90   $192.90  
  Purchase #2 $147.83   8.666%   $160.6409   $160.64   $160.65   $160.60  
  Purchase #3 $27.45   10.601%   $30.36   $30.36   $30.35   $30.40  
  Purchase #4 $167.72   13.824%   $190.9056   $190.91   $190.90   $190.90  
  Purchase #5 $87.75   6.787%   $93.7056   $93.71   $93.70   $93.70  
  Purchase #6 $130.51   3.874%   $135.566   $135.57   $135.55   $135.60  
  Purchase #7 $208.68   5.265%   $219.667   $219.67   $219.65   $219.70  
  7 purchase totals = $939.41       $1,023.7681   $1,023.78   $1,023.70   $1,023.80