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 $155.41   11.708%   $173.6054   $173.61   $173.60   $173.60  
  Purchase #2 $181.42   12.112%   $203.3936   $203.39   $203.40   $203.40  
  Purchase #3 $151.32   10.238%   $166.8121   $166.81   $166.80   $166.80  
  Purchase #4 $99.28   11.584%   $110.7806   $110.78   $110.80   $110.80  
  Purchase #5 $140.63   7.868%   $151.6948   $151.69   $151.70   $151.70  
  Purchase #6 $173.65   8.519%   $188.4432   $188.44   $188.45   $188.40  
  Purchase #7 $35.41   7.616%   $38.1068   $38.11   $38.10   $38.10  
  7 purchase totals = $937.12       $1,032.8365   $1,032.83   $1,032.85   $1,032.80