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 $162.55   9.111%   $177.3599   $177.36   $177.35   $177.40  
  Purchase #2 $31.99   8.180%   $34.6068   $34.61   $34.60   $34.60  
  Purchase #3 $215.58   5.165%   $226.7147   $226.71   $226.70   $226.70  
  Purchase #4 $34.42   4.597%   $36.0023   $36.00   $36.00   $36.00  
  Purchase #5 $152.52   7.322%   $163.6875   $163.69   $163.70   $163.70  
  Purchase #6 $170.71   13.432%   $193.6398   $193.64   $193.65   $193.60  
  Purchase #7 $172.92   8.426%   $187.4902   $187.49   $187.50   $187.50  
  7 purchase totals = $940.69       $1,019.5012   $1,019.50   $1,019.50   $1,019.50