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 $70.90   8.596%   $76.9946   $76.99   $77.00   $77.00  
  Purchase #2 $172.57   13.864%   $196.4951   $196.50   $196.50   $196.50  
  Purchase #3 $204.92   9.741%   $224.8813   $224.88   $224.90   $224.90  
  Purchase #4 $24.69   7.410%   $26.5195   $26.52   $26.50   $26.50  
  Purchase #5 $104.76   7.867%   $113.0015   $113.00   $113.00   $113.00  
  Purchase #6 $140.81   4.752%   $147.5013   $147.50   $147.50   $147.50  
  Purchase #7 $248.52   9.755%   $272.7631   $272.76   $272.75   $272.80  
  7 purchase totals = $967.17       $1,058.1564   $1,058.15   $1,058.15   $1,058.20