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 $151.25   10.573%   $167.2417   $167.24   $167.25   $167.20  
  Purchase #2 $186.53   9.209%   $203.7075   $203.71   $203.70   $203.70  
  Purchase #3 $155.55   4.348%   $162.3133   $162.31   $162.30   $162.30  
  Purchase #4 $16.29   8.446%   $17.6659   $17.67   $17.65   $17.70  
  Purchase #5 $137.26   5.113%   $144.2781   $144.28   $144.30   $144.30  
  Purchase #6 $242.84   8.381%   $263.1924   $263.19   $263.20   $263.20  
  Purchase #7 $98.41   6.517%   $104.8234   $104.82   $104.80   $104.80  
  7 purchase totals = $988.13       $1,063.2223   $1,063.22   $1,063.20   $1,063.20