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 $66.44   12.797%   $74.9423   $74.94   $74.95   $74.90  
  Purchase #2 $201.76   4.753%   $211.3497   $211.35   $211.35   $211.30  
  Purchase #3 $243.70   11.827%   $272.5224   $272.52   $272.50   $272.50  
  Purchase #4 $49.95   10.618%   $55.2537   $55.25   $55.25   $55.30  
  Purchase #5 $142.26   10.328%   $156.9526   $156.95   $156.95   $157.00  
  Purchase #6 $5.76   8.625%   $6.2568   $6.26   $6.25   $6.30  
  Purchase #7 $34.98   11.233%   $38.9093   $38.91   $38.90   $38.90  
  7 purchase totals = $744.85       $816.1868   $816.18   $816.15   $816.20