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 $219.75   8.614%   $238.6793   $238.68   $238.70   $238.70  
  Purchase #2 $88.97   9.506%   $97.4275   $97.43   $97.45   $97.40  
  Purchase #3 $166.43   4.616%   $174.1124   $174.11   $174.10   $174.10  
  Purchase #4 $160.86   10.363%   $177.5299   $177.53   $177.55   $177.50  
  Purchase #5 $89.66   8.727%   $97.4846   $97.48   $97.50   $97.50  
  Purchase #6 $25.61   3.592%   $26.5299   $26.53   $26.55   $26.50  
  Purchase #7 $170.44   13.118%   $192.7983   $192.80   $192.80   $192.80  
  7 purchase totals = $921.72       $1,004.5619   $1,004.56   $1,004.65   $1,004.50