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 $36.36   5.459%   $38.3449   $38.34   $38.35   $38.30  
  Purchase #2 $215.94   9.728%   $236.9466   $236.95   $236.95   $236.90  
  Purchase #3 $158.83   9.653%   $174.1619   $174.16   $174.15   $174.20  
  Purchase #4 $174.78   5.203%   $183.8738   $183.87   $183.85   $183.90  
  Purchase #5 $73.49   4.840%   $77.0469   $77.05   $77.05   $77.00  
  Purchase #6 $162.70   5.505%   $171.6566   $171.66   $171.65   $171.70  
  Purchase #7 $170.49   10.289%   $188.0317   $188.03   $188.05   $188.00  
  7 purchase totals = $992.59       $1,070.0624   $1,070.06   $1,070.05   $1,070.00