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 $53.87   13.561%   $61.1753   $61.18   $61.20   $61.20  
  Purchase #2 $222.33   5.629%   $234.845   $234.85   $234.85   $234.80  
  Purchase #3 $114.87   4.641%   $120.2011   $120.20   $120.20   $120.20  
  Purchase #4 $84.98   4.127%   $88.4871   $88.49   $88.50   $88.50  
  Purchase #5 $113.79   4.293%   $118.675   $118.68   $118.70   $118.70  
  Purchase #6 $77.90   10.591%   $86.1504   $86.15   $86.15   $86.20  
  Purchase #7 $108.70   6.823%   $116.1166   $116.12   $116.10   $116.10  
  7 purchase totals = $776.44       $825.6505   $825.67   $825.70   $825.70