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 $85.84   8.283%   $92.9501   $92.95   $92.95   $93.00  
  Purchase #2 $224.64   11.688%   $250.8959   $250.90   $250.90   $250.90  
  Purchase #3 $211.99   7.791%   $228.5061   $228.51   $228.50   $228.50  
  Purchase #4 $142.51   6.212%   $151.3627   $151.36   $151.35   $151.40  
  Purchase #5 $10.52   9.784%   $11.5493   $11.55   $11.55   $11.50  
  Purchase #6 $37.50   3.523%   $38.8211   $38.82   $38.80   $38.80  
  Purchase #7 $196.27   8.199%   $212.3622   $212.36   $212.35   $212.40  
  7 purchase totals = $909.27       $986.4474   $986.45   $986.40   $986.50