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 $93.58   4.262%   $97.5684   $97.57   $97.55   $97.60  
  Purchase #2 $75.70   3.393%   $78.2685   $78.27   $78.25   $78.30  
  Purchase #3 $249.82   13.276%   $282.9861   $282.99   $283.00   $283.00  
  Purchase #4 $12.93   13.334%   $14.6541   $14.65   $14.65   $14.70  
  Purchase #5 $110.40   7.706%   $118.9074   $118.91   $118.90   $118.90  
  Purchase #6 $199.52   4.473%   $208.4445   $208.44   $208.45   $208.40  
  Purchase #7 $5.61   4.492%   $5.862   $5.86   $5.85   $5.90  
  7 purchase totals = $747.56       $806.6910   $806.69   $806.65   $806.80