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 $57.35   11.665%   $64.0399   $64.04   $64.05   $64.00  
  Purchase #2 $231.49   13.735%   $263.2852   $263.29   $263.30   $263.30  
  Purchase #3 $182.72   6.122%   $193.9061   $193.91   $193.90   $193.90  
  Purchase #4 $248.63   6.214%   $264.0799   $264.08   $264.10   $264.10  
  Purchase #5 $167.43   11.412%   $186.5371   $186.54   $186.55   $186.50  
  Purchase #6 $27.90   4.373%   $29.1201   $29.12   $29.10   $29.10  
  Purchase #7 $44.49   8.816%   $48.4122   $48.41   $48.40   $48.40  
  7 purchase totals = $960.01       $1,049.3805   $1,049.39   $1,049.40   $1,049.30