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 $85.88   11.618%   $95.8575   $95.86   $95.85   $95.90  
  Purchase #2 $152.83   9.225%   $166.9286   $166.93   $166.95   $166.90  
  Purchase #3 $231.56   6.562%   $246.755   $246.76   $246.75   $246.80  
  Purchase #4 $238.39   11.623%   $266.0981   $266.10   $266.10   $266.10  
  Purchase #5 $82.93   13.503%   $94.128   $94.13   $94.15   $94.10  
  Purchase #6 $8.31   13.603%   $9.4404   $9.44   $9.45   $9.40  
  Purchase #7 $176.69   9.407%   $193.3112   $193.31   $193.30   $193.30  
  7 purchase totals = $976.59       $1,072.5188   $1,072.53   $1,072.55   $1,072.50