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 $122.42   3.710%   $126.9618   $126.96   $126.95   $127.00  
  Purchase #2 $153.89   3.608%   $159.4424   $159.44   $159.45   $159.40  
  Purchase #3 $14.51   3.467%   $15.0131   $15.01   $15.00   $15.00  
  Purchase #4 $183.29   3.239%   $189.2268   $189.23   $189.25   $189.20  
  Purchase #5 $222.95   11.445%   $248.4666   $248.47   $248.45   $248.50  
  Purchase #6 $151.54   5.263%   $159.5156   $159.52   $159.50   $159.50  
  Purchase #7 $134.29   11.779%   $150.108   $150.11   $150.10   $150.10  
  7 purchase totals = $982.89       $1,048.7343   $1,048.74   $1,048.70   $1,048.70