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 $27.33   7.371%   $29.3445   $29.34   $29.35   $29.30  
  Purchase #2 $181.94   10.723%   $201.4494   $201.45   $201.45   $201.40  
  Purchase #3 $166.92   5.720%   $176.4678   $176.47   $176.45   $176.50  
  Purchase #4 $172.84   5.349%   $182.0852   $182.09   $182.10   $182.10  
  Purchase #5 $59.79   11.766%   $66.8249   $66.82   $66.80   $66.80  
  Purchase #6 $188.98   8.470%   $204.9866   $204.99   $205.00   $205.00  
  Purchase #7 $107.47   3.845%   $111.6022   $111.60   $111.60   $111.60  
  7 purchase totals = $905.27       $972.7606   $972.76   $972.75   $972.70