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 $234.28   6.144%   $248.6742   $248.67   $248.65   $248.70  
  Purchase #2 $218.43   4.134%   $227.4599   $227.46   $227.45   $227.50  
  Purchase #3 $152.83   3.127%   $157.609   $157.61   $157.60   $157.60  
  Purchase #4 $202.59   8.293%   $219.3908   $219.39   $219.40   $219.40  
  Purchase #5 $149.30   6.387%   $158.8358   $158.84   $158.85   $158.80  
  Purchase #6 $240.56   11.578%   $268.412   $268.41   $268.40   $268.40  
  Purchase #7 $153.53   6.732%   $163.8656   $163.87   $163.85   $163.90  
  7 purchase totals = $1,351.52       $1,444.2473   $1,444.25   $1,444.20   $1,444.30