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 $134.84   9.549%   $147.7159   $147.72   $147.70   $147.70  
  Purchase #2 $98.41   12.313%   $110.5272   $110.53   $110.55   $110.50  
  Purchase #3 $66.51   8.731%   $72.317   $72.32   $72.30   $72.30  
  Purchase #4 $89.56   5.573%   $94.5512   $94.55   $94.55   $94.60  
  Purchase #5 $193.73   3.299%   $200.1212   $200.12   $200.10   $200.10  
  Purchase #6 $192.78   10.610%   $213.234   $213.23   $213.25   $213.20  
  Purchase #7 $22.26   7.787%   $23.9934   $23.99   $24.00   $24.00  
  7 purchase totals = $798.09       $862.4599   $862.46   $862.45   $862.40