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 $68.66   7.679%   $73.9324   $73.93   $73.95   $73.90  
  Purchase #2 $133.62   3.754%   $138.6361   $138.64   $138.65   $138.60  
  Purchase #3 $162.46   3.449%   $168.0632   $168.06   $168.05   $168.10  
  Purchase #4 $212.92   10.735%   $235.777   $235.78   $235.80   $235.80  
  Purchase #5 $24.53   6.474%   $26.1181   $26.12   $26.10   $26.10  
  Purchase #6 $93.69   8.440%   $101.5974   $101.60   $101.60   $101.60  
  Purchase #7 $74.40   7.453%   $79.945   $79.95   $79.95   $79.90  
  7 purchase totals = $770.28       $824.0692   $824.08   $824.10   $824.00