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 $34.83   3.469%   $36.0383   $36.04   $36.05   $36.00  
  Purchase #2 $211.74   9.669%   $232.2131   $232.21   $232.20   $232.20  
  Purchase #3 $20.69   12.519%   $23.2802   $23.28   $23.30   $23.30  
  Purchase #4 $72.58   10.534%   $80.2256   $80.23   $80.25   $80.20  
  Purchase #5 $128.31   7.494%   $137.9256   $137.93   $137.95   $137.90  
  Purchase #6 $233.26   7.470%   $250.6845   $250.68   $250.70   $250.70  
  Purchase #7 $128.27   5.568%   $135.4121   $135.41   $135.40   $135.40  
  7 purchase totals = $829.68       $895.7794   $895.78   $895.85   $895.70