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 $171.73   12.201%   $192.6828   $192.68   $192.70   $192.70  
  Purchase #2 $39.58   7.372%   $42.4978   $42.50   $42.50   $42.50  
  Purchase #3 $60.81   8.128%   $65.7526   $65.75   $65.75   $65.80  
  Purchase #4 $190.31   8.163%   $205.845   $205.85   $205.85   $205.80  
  Purchase #5 $133.44   7.277%   $143.1504   $143.15   $143.15   $143.20  
  Purchase #6 $119.49   9.252%   $130.5452   $130.55   $130.55   $130.50  
  Purchase #7 $211.83   11.776%   $236.7751   $236.78   $236.80   $236.80  
  7 purchase totals = $927.19       $1,017.2489   $1,017.26   $1,017.30   $1,017.30