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 $237.34   8.363%   $257.1887   $257.19   $257.20   $257.20  
  Purchase #2 $125.82   8.341%   $136.3146   $136.31   $136.30   $136.30  
  Purchase #3 $81.65   8.177%   $88.3265   $88.33   $88.35   $88.30  
  Purchase #4 $117.54   3.282%   $121.3977   $121.40   $121.40   $121.40  
  Purchase #5 $145.89   3.824%   $151.4688   $151.47   $151.45   $151.50  
  Purchase #6 $80.73   6.501%   $85.9783   $85.98   $86.00   $86.00  
  Purchase #7 $166.40   11.605%   $185.7107   $185.71   $185.70   $185.70  
  7 purchase totals = $955.37       $1,026.3853   $1,026.39   $1,026.40   $1,026.40