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 $51.59   8.470%   $55.9597   $55.96   $55.95   $56.00  
  Purchase #2 $249.98   6.826%   $267.0436   $267.04   $267.05   $267.00  
  Purchase #3 $119.58   8.218%   $129.4071   $129.41   $129.40   $129.40  
  Purchase #4 $99.26   4.549%   $103.7753   $103.78   $103.80   $103.80  
  Purchase #5 $170.86   3.603%   $177.0161   $177.02   $177.00   $177.00  
  Purchase #6 $86.28   6.859%   $92.1979   $92.20   $92.20   $92.20  
  Purchase #7 $203.61   3.691%   $211.1252   $211.13   $211.15   $211.10  
  7 purchase totals = $981.16       $1,036.5249   $1,036.54   $1,036.55   $1,036.50