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 $132.36   11.258%   $147.2611   $147.26   $147.25   $147.30  
  Purchase #2 $206.88   13.641%   $235.1005   $235.10   $235.10   $235.10  
  Purchase #3 $196.29   6.161%   $208.3834   $208.38   $208.40   $208.40  
  Purchase #4 $32.37   6.310%   $34.4125   $34.41   $34.40   $34.40  
  Purchase #5 $216.97   11.231%   $241.3379   $241.34   $241.35   $241.30  
  Purchase #6 $198.96   7.258%   $213.4005   $213.40   $213.40   $213.40  
  Purchase #7 $11.81   9.347%   $12.9139   $12.91   $12.90   $12.90  
  7 purchase totals = $995.64       $1,092.8098   $1,092.80   $1,092.80   $1,092.80