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 $209.34   13.163%   $236.8954   $236.90   $236.90   $236.90  
  Purchase #2 $126.30   4.281%   $131.7069   $131.71   $131.70   $131.70  
  Purchase #3 $208.79   5.121%   $219.4821   $219.48   $219.50   $219.50  
  Purchase #4 $87.67   8.347%   $94.9878   $94.99   $95.00   $95.00  
  Purchase #5 $132.96   9.356%   $145.3997   $145.40   $145.40   $145.40  
  Purchase #6 $238.79   3.108%   $246.2116   $246.21   $246.20   $246.20  
  Purchase #7 $238.30   5.822%   $252.1738   $252.17   $252.15   $252.20  
  7 purchase totals = $1,242.15       $1,326.8573   $1,326.86   $1,326.85   $1,326.90