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 $165.48   11.479%   $184.4754   $184.48   $184.50   $184.50  
  Purchase #2 $192.99   11.818%   $215.7976   $215.80   $215.80   $215.80  
  Purchase #3 $94.58   8.384%   $102.5096   $102.51   $102.50   $102.50  
  Purchase #4 $134.63   9.226%   $147.051   $147.05   $147.05   $147.10  
  Purchase #5 $53.66   13.579%   $60.9465   $60.95   $60.95   $60.90  
  Purchase #6 $244.33   11.776%   $273.1023   $273.10   $273.10   $273.10  
  Purchase #7 $106.51   6.114%   $113.022   $113.02   $113.00   $113.00  
  7 purchase totals = $992.18       $1,096.9044   $1,096.91   $1,096.90   $1,096.90