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 $90.63   12.426%   $101.8917   $101.89   $101.90   $101.90  
  Purchase #2 $173.97   8.179%   $188.199   $188.20   $188.20   $188.20  
  Purchase #3 $41.58   4.267%   $43.3542   $43.35   $43.35   $43.40  
  Purchase #4 $237.80   10.845%   $263.5894   $263.59   $263.60   $263.60  
  Purchase #5 $166.94   10.626%   $184.679   $184.68   $184.70   $184.70  
  Purchase #6 $248.54   9.674%   $272.5838   $272.58   $272.60   $272.60  
  Purchase #7 $232.91   5.430%   $245.557   $245.56   $245.55   $245.60  
  7 purchase totals = $1,192.37       $1,299.8541   $1,299.85   $1,299.90   $1,300.00