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 $61.84   12.255%   $69.4185   $69.42   $69.40   $69.40  
  Purchase #2 $173.25   6.623%   $184.7243   $184.72   $184.70   $184.70  
  Purchase #3 $235.48   4.719%   $246.5923   $246.59   $246.60   $246.60  
  Purchase #4 $197.78   6.253%   $210.1472   $210.15   $210.15   $210.10  
  Purchase #5 $123.25   8.194%   $133.3491   $133.35   $133.35   $133.30  
  Purchase #6 $172.67   9.665%   $189.3586   $189.36   $189.35   $189.40  
  Purchase #7 $209.60   7.867%   $226.0892   $226.09   $226.10   $226.10  
  7 purchase totals = $1,173.87       $1,259.6792   $1,259.68   $1,259.65   $1,259.60