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 $248.93   9.652%   $272.9567   $272.96   $272.95   $273.00  
  Purchase #2 $7.81   13.645%   $8.8757   $8.88   $8.90   $8.90  
  Purchase #3 $41.58   4.522%   $43.4602   $43.46   $43.45   $43.50  
  Purchase #4 $48.59   12.691%   $54.7566   $54.76   $54.75   $54.80  
  Purchase #5 $118.33   3.679%   $122.6834   $122.68   $122.70   $122.70  
  Purchase #6 $85.82   7.204%   $92.0025   $92.00   $92.00   $92.00  
  Purchase #7 $146.99   10.741%   $162.7782   $162.78   $162.80   $162.80  
  7 purchase totals = $698.05       $757.5133   $757.52   $757.55   $757.70