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 $188.29   12.102%   $211.0769   $211.08   $211.10   $211.10  
  Purchase #2 $227.97   4.554%   $238.3518   $238.35   $238.35   $238.40  
  Purchase #3 $85.85   6.325%   $91.28   $91.28   $91.30   $91.30  
  Purchase #4 $222.26   5.858%   $235.28   $235.28   $235.30   $235.30  
  Purchase #5 $114.72   7.242%   $123.028   $123.03   $123.05   $123.00  
  Purchase #6 $215.87   9.556%   $236.4985   $236.50   $236.50   $236.50  
  Purchase #7 $214.85   7.606%   $231.1915   $231.19   $231.20   $231.20  
  7 purchase totals = $1,269.81       $1,366.7067   $1,366.71   $1,366.80   $1,366.80