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 $111.84   6.157%   $118.726   $118.73   $118.75   $118.70  
  Purchase #2 $146.68   3.422%   $151.6994   $151.70   $151.70   $151.70  
  Purchase #3 $120.65   11.187%   $134.1471   $134.15   $134.15   $134.10  
  Purchase #4 $186.52   4.812%   $195.4953   $195.50   $195.50   $195.50  
  Purchase #5 $78.77   10.769%   $87.2527   $87.25   $87.25   $87.30  
  Purchase #6 $70.52   13.257%   $79.8688   $79.87   $79.85   $79.90  
  Purchase #7 $206.88   13.538%   $234.8874   $234.89   $234.90   $234.90  
  7 purchase totals = $921.86       $1,002.0767   $1,002.09   $1,002.10   $1,002.10