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 $43.64   12.473%   $49.0832   $49.08   $49.10   $49.10  
  Purchase #2 $171.93   13.569%   $195.2592   $195.26   $195.25   $195.30  
  Purchase #3 $32.56   6.112%   $34.5501   $34.55   $34.55   $34.60  
  Purchase #4 $67.49   3.175%   $69.6328   $69.63   $69.65   $69.60  
  Purchase #5 $228.27   13.116%   $258.2099   $258.21   $258.20   $258.20  
  Purchase #6 $160.29   9.463%   $175.4582   $175.46   $175.45   $175.50  
  Purchase #7 $213.31   5.542%   $225.1316   $225.13   $225.15   $225.10  
  7 purchase totals = $917.49       $1,007.3250   $1,007.32   $1,007.35   $1,007.40