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 $168.90   10.690%   $186.9554   $186.96   $186.95   $187.00  
  Purchase #2 $37.87   9.820%   $41.5888   $41.59   $41.60   $41.60  
  Purchase #3 $214.92   9.660%   $235.6813   $235.68   $235.70   $235.70  
  Purchase #4 $72.51   10.269%   $79.9561   $79.96   $79.95   $80.00  
  Purchase #5 $219.62   6.844%   $234.6508   $234.65   $234.65   $234.70  
  Purchase #6 $42.59   4.339%   $44.438   $44.44   $44.45   $44.40  
  Purchase #7 $56.93   11.237%   $63.3272   $63.33   $63.35   $63.30  
  7 purchase totals = $813.34       $886.5976   $886.61   $886.65   $886.70