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 $59.58   8.221%   $64.4781   $64.48   $64.50   $64.50  
  Purchase #2 $226.76   3.467%   $234.6218   $234.62   $234.60   $234.60  
  Purchase #3 $233.71   8.180%   $252.8275   $252.83   $252.85   $252.80  
  Purchase #4 $113.35   13.489%   $128.6398   $128.64   $128.65   $128.60  
  Purchase #5 $161.71   11.645%   $180.5411   $180.54   $180.55   $180.50  
  Purchase #6 $172.28   5.360%   $181.5142   $181.51   $181.50   $181.50  
  Purchase #7 $223.66   13.336%   $253.4873   $253.49   $253.50   $253.50  
  7 purchase totals = $1,191.05       $1,296.1098   $1,296.11   $1,296.15   $1,296.00