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 $216.87   10.447%   $239.5264   $239.53   $239.55   $239.50  
  Purchase #2 $177.57   13.444%   $201.4425   $201.44   $201.45   $201.40  
  Purchase #3 $67.33   6.645%   $71.8041   $71.80   $71.80   $71.80  
  Purchase #4 $191.44   12.181%   $214.7593   $214.76   $214.75   $214.80  
  Purchase #5 $108.37   8.232%   $117.291   $117.29   $117.30   $117.30  
  Purchase #6 $37.44   10.611%   $41.4128   $41.41   $41.40   $41.40  
  Purchase #7 $231.31   12.556%   $260.3533   $260.35   $260.35   $260.40  
  7 purchase totals = $1,030.33       $1,146.5894   $1,146.58   $1,146.60   $1,146.60