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 $248.32   4.395%   $259.2337   $259.23   $259.25   $259.20  
  Purchase #2 $112.67   9.426%   $123.2903   $123.29   $123.30   $123.30  
  Purchase #3 $205.93   9.702%   $225.9093   $225.91   $225.90   $225.90  
  Purchase #4 $40.42   8.843%   $43.9943   $43.99   $44.00   $44.00  
  Purchase #5 $24.46   10.779%   $27.0965   $27.10   $27.10   $27.10  
  Purchase #6 $20.99   10.337%   $23.1597   $23.16   $23.15   $23.20  
  Purchase #7 $53.70   8.590%   $58.3128   $58.31   $58.30   $58.30  
  7 purchase totals = $706.49       $760.9966   $760.99   $761.00   $761.00