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 $201.49   7.316%   $216.231   $216.23   $216.25   $216.20  
  Purchase #2 $101.82   12.415%   $114.461   $114.46   $114.45   $114.50  
  Purchase #3 $37.72   3.494%   $39.0379   $39.04   $39.05   $39.00  
  Purchase #4 $64.96   11.571%   $72.4765   $72.48   $72.50   $72.50  
  Purchase #5 $75.46   3.351%   $77.9887   $77.99   $78.00   $78.00  
  Purchase #6 $240.37   11.509%   $268.0342   $268.03   $268.05   $268.00  
  Purchase #7 $60.79   13.190%   $68.8082   $68.81   $68.80   $68.80  
  7 purchase totals = $782.61       $857.0375   $857.04   $857.10   $857.00