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 $58.41   12.422%   $65.6657   $65.67   $65.65   $65.70  
  Purchase #2 $209.32   13.541%   $237.664   $237.66   $237.65   $237.70  
  Purchase #3 $31.57   5.564%   $33.3266   $33.33   $33.35   $33.30  
  Purchase #4 $76.25   11.223%   $84.8075   $84.81   $84.80   $84.80  
  Purchase #5 $226.64   6.597%   $241.5914   $241.59   $241.60   $241.60  
  Purchase #6 $23.36   11.461%   $26.0373   $26.04   $26.05   $26.00  
  Purchase #7 $222.71   11.407%   $248.1145   $248.11   $248.10   $248.10  
  7 purchase totals = $848.26       $937.2070   $937.21   $937.20   $937.20