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 $57.54   12.174%   $64.5449   $64.54   $64.55   $64.50  
  Purchase #2 $39.59   8.773%   $43.0632   $43.06   $43.05   $43.10  
  Purchase #3 $24.41   8.688%   $26.5307   $26.53   $26.55   $26.50  
  Purchase #4 $246.44   5.642%   $260.3441   $260.34   $260.35   $260.30  
  Purchase #5 $71.41   11.610%   $79.7007   $79.70   $79.70   $79.70  
  Purchase #6 $63.58   4.644%   $66.5327   $66.53   $66.55   $66.50  
  Purchase #7 $217.47   5.647%   $229.7505   $229.75   $229.75   $229.80  
  7 purchase totals = $720.44       $770.4668   $770.45   $770.50   $770.40