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 $246.86   9.112%   $269.3539   $269.35   $269.35   $269.40  
  Purchase #2 $89.96   5.511%   $94.9177   $94.92   $94.90   $94.90  
  Purchase #3 $39.26   4.719%   $41.1127   $41.11   $41.10   $41.10  
  Purchase #4 $223.69   13.356%   $253.566   $253.57   $253.55   $253.60  
  Purchase #5 $245.31   11.467%   $273.4397   $273.44   $273.45   $273.40  
  Purchase #6 $121.56   10.734%   $134.6083   $134.61   $134.60   $134.60  
  Purchase #7 $28.48   7.209%   $30.5331   $30.53   $30.55   $30.50  
  7 purchase totals = $995.12       $1,097.5314   $1,097.53   $1,097.50   $1,097.50