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 $39.93   9.164%   $43.5892   $43.59   $43.60   $43.60  
  Purchase #2 $176.34   13.104%   $199.4476   $199.45   $199.45   $199.40  
  Purchase #3 $141.93   5.151%   $149.2408   $149.24   $149.25   $149.20  
  Purchase #4 $188.44   12.388%   $211.7839   $211.78   $211.80   $211.80  
  Purchase #5 $186.34   6.440%   $198.3403   $198.34   $198.35   $198.30  
  Purchase #6 $173.58   5.431%   $183.0071   $183.01   $183.00   $183.00  
  Purchase #7 $200.47   7.136%   $214.7755   $214.78   $214.80   $214.80  
  7 purchase totals = $1,107.03       $1,200.1844   $1,200.19   $1,200.25   $1,200.10