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 $119.81   7.209%   $128.4471   $128.45   $128.45   $128.40  
  Purchase #2 $117.63   5.269%   $123.8279   $123.83   $123.85   $123.80  
  Purchase #3 $68.48   10.284%   $75.5225   $75.52   $75.50   $75.50  
  Purchase #4 $59.80   5.681%   $63.1972   $63.20   $63.20   $63.20  
  Purchase #5 $220.39   12.727%   $248.439   $248.44   $248.45   $248.40  
  Purchase #6 $163.55   12.694%   $184.311   $184.31   $184.30   $184.30  
  Purchase #7 $131.94   5.351%   $139.0001   $139.00   $139.00   $139.00  
  7 purchase totals = $881.60       $962.7448   $962.75   $962.75   $962.60