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 $31.50   9.615%   $34.5287   $34.53   $34.55   $34.50  
  Purchase #2 $229.97   10.445%   $253.9904   $253.99   $254.00   $254.00  
  Purchase #3 $167.54   5.392%   $176.5738   $176.57   $176.55   $176.60  
  Purchase #4 $225.77   5.628%   $238.4763   $238.48   $238.50   $238.50  
  Purchase #5 $97.30   5.355%   $102.5104   $102.51   $102.50   $102.50  
  Purchase #6 $121.78   3.393%   $125.912   $125.91   $125.90   $125.90  
  Purchase #7 $214.85   7.493%   $230.9487   $230.95   $230.95   $230.90  
  7 purchase totals = $1,088.71       $1,162.9403   $1,162.94   $1,162.95   $1,162.90