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 $46.42   8.471%   $50.3522   $50.35   $50.35   $50.40  
  Purchase #2 $207.46   10.860%   $229.9902   $229.99   $230.00   $230.00  
  Purchase #3 $102.78   10.637%   $113.7127   $113.71   $113.70   $113.70  
  Purchase #4 $172.77   7.715%   $186.0992   $186.10   $186.10   $186.10  
  Purchase #5 $208.78   9.496%   $228.6057   $228.61   $228.60   $228.60  
  Purchase #6 $56.90   5.395%   $59.9698   $59.97   $59.95   $60.00  
  Purchase #7 $192.26   8.618%   $208.829   $208.83   $208.85   $208.80  
  7 purchase totals = $987.37       $1,077.5588   $1,077.56   $1,077.55   $1,077.60