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 $233.65   10.742%   $258.7487   $258.75   $258.75   $258.70  
  Purchase #2 $246.85   8.830%   $268.6469   $268.65   $268.65   $268.60  
  Purchase #3 $237.78   11.626%   $265.4243   $265.42   $265.40   $265.40  
  Purchase #4 $14.56   12.149%   $16.3289   $16.33   $16.35   $16.30  
  Purchase #5 $173.25   6.659%   $184.7867   $184.79   $184.80   $184.80  
  Purchase #6 $234.87   7.584%   $252.6825   $252.68   $252.70   $252.70  
  Purchase #7 $84.95   13.225%   $96.1846   $96.18   $96.20   $96.20  
  7 purchase totals = $1,225.91       $1,342.8026   $1,342.80   $1,342.85   $1,342.70