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 $150.79   8.468%   $163.5589   $163.56   $163.55   $163.60  
  Purchase #2 $227.97   11.582%   $254.3735   $254.37   $254.35   $254.40  
  Purchase #3 $244.37   6.109%   $259.2986   $259.30   $259.30   $259.30  
  Purchase #4 $243.79   5.221%   $256.5183   $256.52   $256.50   $256.50  
  Purchase #5 $30.79   13.111%   $34.8269   $34.83   $34.85   $34.80  
  Purchase #6 $40.83   10.610%   $45.1621   $45.16   $45.15   $45.20  
  Purchase #7 $237.88   4.553%   $248.7107   $248.71   $248.70   $248.70  
  7 purchase totals = $1,176.42       $1,262.4490   $1,262.45   $1,262.40   $1,262.50