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 $229.48   9.492%   $251.2622   $251.26   $251.25   $251.30  
  Purchase #2 $62.54   4.295%   $65.2261   $65.23   $65.25   $65.20  
  Purchase #3 $186.56   4.149%   $194.3004   $194.30   $194.30   $194.30  
  Purchase #4 $121.25   13.224%   $137.2841   $137.28   $137.30   $137.30  
  Purchase #5 $85.63   12.745%   $96.5435   $96.54   $96.55   $96.50  
  Purchase #6 $99.86   6.826%   $106.6764   $106.68   $106.70   $106.70  
  Purchase #7 $26.42   3.387%   $27.3148   $27.31   $27.30   $27.30  
  7 purchase totals = $811.74       $878.6075   $878.60   $878.65   $878.60