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 $237.81   11.704%   $265.6433   $265.64   $265.65   $265.60  
  Purchase #2 $68.35   10.365%   $75.4345   $75.43   $75.45   $75.40  
  Purchase #3 $240.44   13.432%   $272.7359   $272.74   $272.75   $272.70  
  Purchase #4 $59.28   9.317%   $64.8031   $64.80   $64.80   $64.80  
  Purchase #5 $44.58   3.758%   $46.2553   $46.26   $46.25   $46.30  
  Purchase #6 $231.41   11.245%   $257.4321   $257.43   $257.45   $257.40  
  Purchase #7 $61.28   6.472%   $65.246   $65.25   $65.25   $65.20  
  7 purchase totals = $943.15       $1,047.5502   $1,047.55   $1,047.60   $1,047.40