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 $152.36   7.582%   $163.9119   $163.91   $163.90   $163.90  
  Purchase #2 $249.55   11.128%   $277.3199   $277.32   $277.30   $277.30  
  Purchase #3 $192.56   11.426%   $214.5619   $214.56   $214.55   $214.60  
  Purchase #4 $91.90   13.792%   $104.5748   $104.57   $104.55   $104.60  
  Purchase #5 $51.62   10.287%   $56.9301   $56.93   $56.95   $56.90  
  Purchase #6 $208.81   5.826%   $220.9753   $220.98   $221.00   $221.00  
  Purchase #7 $147.84   12.321%   $166.0554   $166.06   $166.05   $166.10  
  7 purchase totals = $1,094.64       $1,204.3293   $1,204.33   $1,204.30   $1,204.40