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 $246.41   12.628%   $277.5267   $277.53   $277.55   $277.50  
  Purchase #2 $66.42   6.862%   $70.9777   $70.98   $71.00   $71.00  
  Purchase #3 $176.48   8.548%   $191.5655   $191.57   $191.55   $191.60  
  Purchase #4 $114.93   5.857%   $121.6615   $121.66   $121.65   $121.70  
  Purchase #5 $52.91   5.477%   $55.8079   $55.81   $55.80   $55.80  
  Purchase #6 $213.78   8.171%   $231.248   $231.25   $231.25   $231.20  
  Purchase #7 $183.65   11.279%   $204.3639   $204.36   $204.35   $204.40  
  7 purchase totals = $1,054.58       $1,153.1512   $1,153.16   $1,153.15   $1,153.20