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 $131.75   9.304%   $144.008   $144.01   $144.00   $144.00  
  Purchase #2 $54.39   4.724%   $56.9594   $56.96   $56.95   $57.00  
  Purchase #3 $161.79   8.403%   $175.3852   $175.39   $175.40   $175.40  
  Purchase #4 $47.47   3.737%   $49.244   $49.24   $49.25   $49.20  
  Purchase #5 $184.31   4.546%   $192.6887   $192.69   $192.70   $192.70  
  Purchase #6 $202.34   6.303%   $215.0935   $215.09   $215.10   $215.10  
  Purchase #7 $88.70   5.611%   $93.677   $93.68   $93.70   $93.70  
  7 purchase totals = $870.75       $927.0558   $927.06   $927.10   $927.10