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 $184.50   13.776%   $209.9167   $209.92   $209.90   $209.90  
  Purchase #2 $86.66   7.732%   $93.3606   $93.36   $93.35   $93.40  
  Purchase #3 $33.26   4.139%   $34.6366   $34.64   $34.65   $34.60  
  Purchase #4 $202.80   10.696%   $224.4915   $224.49   $224.50   $224.50  
  Purchase #5 $11.96   4.292%   $12.4733   $12.47   $12.45   $12.50  
  Purchase #6 $188.59   12.576%   $212.3071   $212.31   $212.30   $212.30  
  Purchase #7 $59.89   11.850%   $66.987   $66.99   $67.00   $67.00  
  7 purchase totals = $767.66       $854.1728   $854.18   $854.15   $854.20