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 $237.98   3.369%   $245.9975   $246.00   $246.00   $246.00  
  Purchase #2 $37.33   11.699%   $41.6972   $41.70   $41.70   $41.70  
  Purchase #3 $167.67   8.780%   $182.3914   $182.39   $182.40   $182.40  
  Purchase #4 $226.45   7.455%   $243.3318   $243.33   $243.35   $243.30  
  Purchase #5 $115.26   7.358%   $123.7408   $123.74   $123.75   $123.70  
  Purchase #6 $129.56   4.189%   $134.9873   $134.99   $135.00   $135.00  
  Purchase #7 $36.61   6.253%   $38.8992   $38.90   $38.90   $38.90  
  7 purchase totals = $950.86       $1,011.0452   $1,011.05   $1,011.10   $1,011.00