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 $101.71   10.654%   $112.5462   $112.55   $112.55   $112.50  
  Purchase #2 $219.81   8.139%   $237.7003   $237.70   $237.70   $237.70  
  Purchase #3 $245.64   3.428%   $254.0605   $254.06   $254.05   $254.10  
  Purchase #4 $87.57   8.121%   $94.6816   $94.68   $94.70   $94.70  
  Purchase #5 $96.38   13.175%   $109.0781   $109.08   $109.10   $109.10  
  Purchase #6 $186.81   9.423%   $204.4131   $204.41   $204.40   $204.40  
  Purchase #7 $47.49   3.549%   $49.1754   $49.18   $49.20   $49.20  
  7 purchase totals = $985.41       $1,061.6552   $1,061.66   $1,061.70   $1,061.70