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 $108.56   6.804%   $115.9464   $115.95   $115.95   $115.90  
  Purchase #2 $209.29   3.635%   $216.8977   $216.90   $216.90   $216.90  
  Purchase #3 $250.60   6.482%   $266.8439   $266.84   $266.85   $266.80  
  Purchase #4 $97.79   7.403%   $105.0294   $105.03   $105.05   $105.00  
  Purchase #5 $113.96   6.717%   $121.6147   $121.61   $121.60   $121.60  
  Purchase #6 $19.61   5.329%   $20.655   $20.66   $20.65   $20.70  
  Purchase #7 $152.52   4.625%   $159.5741   $159.57   $159.55   $159.60  
  7 purchase totals = $952.33       $1,006.5612   $1,006.56   $1,006.55   $1,006.50