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 $90.66   4.804%   $95.0153   $95.02   $95.00   $95.00  
  Purchase #2 $61.55   4.840%   $64.529   $64.53   $64.55   $64.50  
  Purchase #3 $192.70   9.470%   $210.9487   $210.95   $210.95   $210.90  
  Purchase #4 $33.63   7.455%   $36.1371   $36.14   $36.15   $36.10  
  Purchase #5 $127.87   6.124%   $135.7008   $135.70   $135.70   $135.70  
  Purchase #6 $239.99   10.615%   $265.4649   $265.46   $265.45   $265.50  
  Purchase #7 $189.55   6.389%   $201.6603   $201.66   $201.65   $201.70  
  7 purchase totals = $935.95       $1,009.4561   $1,009.46   $1,009.45   $1,009.40