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 $85.97   12.270%   $96.5185   $96.52   $96.50   $96.50  
  Purchase #2 $178.35   10.430%   $196.9519   $196.95   $196.95   $197.00  
  Purchase #3 $30.45   9.184%   $33.2465   $33.25   $33.25   $33.20  
  Purchase #4 $14.96   9.412%   $16.368   $16.37   $16.35   $16.40  
  Purchase #5 $165.91   11.387%   $184.8022   $184.80   $184.80   $184.80  
  Purchase #6 $61.51   3.289%   $63.5331   $63.53   $63.55   $63.50  
  Purchase #7 $159.66   4.355%   $166.6132   $166.61   $166.60   $166.60  
  7 purchase totals = $696.81       $758.0334   $758.03   $758.00   $758.00