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 $168.61   10.731%   $186.7035   $186.70   $186.70   $186.70  
  Purchase #2 $90.26   6.778%   $96.3778   $96.38   $96.40   $96.40  
  Purchase #3 $104.37   9.236%   $114.0096   $114.01   $114.00   $114.00  
  Purchase #4 $83.94   4.825%   $87.9901   $87.99   $88.00   $88.00  
  Purchase #5 $34.89   5.379%   $36.7667   $36.77   $36.75   $36.80  
  Purchase #6 $161.33   8.376%   $174.843   $174.84   $174.85   $174.80  
  Purchase #7 $236.85   11.284%   $263.5762   $263.58   $263.60   $263.60  
  7 purchase totals = $880.25       $960.2669   $960.27   $960.30   $960.30