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 $242.54   11.263%   $269.8573   $269.86   $269.85   $269.90  
  Purchase #2 $126.54   6.158%   $134.3323   $134.33   $134.35   $134.30  
  Purchase #3 $79.80   8.775%   $86.8025   $86.80   $86.80   $86.80  
  Purchase #4 $85.32   8.432%   $92.5142   $92.51   $92.50   $92.50  
  Purchase #5 $33.33   7.185%   $35.7248   $35.72   $35.70   $35.70  
  Purchase #6 $218.29   5.860%   $231.0818   $231.08   $231.10   $231.10  
  Purchase #7 $140.56   12.382%   $157.9641   $157.96   $157.95   $158.00  
  7 purchase totals = $926.38       $1,008.2770   $1,008.26   $1,008.25   $1,008.30